Dell Appassure 5 User Guide

							Dell AppAssure User Guide
Version 5.4.3 Revision B109 9 Select the appropriate protection schedule as described below.To use the default protection schedule, in 
the Schedule Settings option, select Default protection.
With a default protection schedule, the Core will take snapshots of all volumes on the protected 
machine once every hour. To change the protection settings at any time after you close the 
wizard, including choosing which volumes to protect, go to the Summary tab for the specific 
protected machine.
•To define a different protection schedule, in the Schedule Settings option, select Custom 
protection.
10 Proceed with your configuration as follows:
•If you selected a Typical configuration for the Protect Machine Wizard and specified default 
protection, then click Finish to confirm your choices, close the wizard, and protect the machine 
you specified.
The first time protection is added for a machine, a base image (that is, a snapshot of all the data 
in the protected volumes) will transfer to the repository on the AppAssure Core following the 
schedule you defined, unless you specified to initially pause protection.
•If you selected a Typical configuration for the Protect Machine Wizard and specified custom 
protection, then click Next to set up a custom protection schedule. For details on defining a 
custom protection schedule, see Creating custom protection schedules.
•If you selected Advanced configuration for the Protect Machine Wizard, and default protection, 
then click Next and proceed to Step 14 to see repository and encryption options.
•If you selected Advanced configuration for the Protect Machine Wizard and specified custom 
protection, then click Next and proceed to Step 11 to choose which volumes to protect.
11 On the Protection Volumes page, select which volumes you want to protect. If any volumes are listed 
that you do not want to include in protection, click in the Check column to clear the selection. Then 
click Next.
12 On the Protection Schedule page, define a custom protection schedule and then click Next. For details 
on defining a custom protection schedule, see Creating custom protection schedules.
13 If you already have repository information configured, the Encryption page appears. Proceed to Step 19 
14 On the Repository page, do one of the following:
•If you want to store the data from this machine for protection in an existing repository, then 
select Use an existing repository, select the appropriate repository from the list, and then click 
Next.
The Encryption page appears. Skip to Step 19 to optionally define encryption.
•If you want to create a new storage location on the Core, then do the following:
aSelect Create a Repository.
b On the Repository page, in the Name field, specify the name of the repository you want to 
create.
This is typically the word Repository and an index number, which corresponds to the 
number of the new repository (for example, Repository1
). You can change the name as 
needed. You can enter up to 40 characters. This name must be unique for this core.
NOTE: Typically, it is good practice to protect, at minimum, the System Reserved volume and the 
volume with the operating system (typically the C drive).
NOTE: When specifying the repository name, use only alphanumeric characters or the 
hyphen. No other symbols or punctuation characters are permitted. Do not use letter 
combinations that specify commands or reserved words (such as con, prn, aux, or null) or 
that represent ports (such as com or lpt). 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B110 cIn the Location field, enter a directory path for the repository. For example, on a local 
computer, type C:\Repository. This location must be unique for this core. If storing your 
repository on a shared drive, enter in format \\servername\sharename.
d If storing the repository on a shared volume, in the User Name field, enter the user name 
with privileges to access the shared drive, and in the Password field, enter the password 
for this user.
eIn the Metadata path field, enter the path where you want metadata to be stored. This 
should be a subdirectory of the storage location. For example, if the storage location is 
C:\Repository, type C:\Repository\Metadata. This must be a unique path for this core.
15 When you have entered all required data for the Repository page, click Next.
The Repository Configuration page appears.
16 Specify the size of the repository.
17 To specify bytes per sector, bytes per record, or control the write caching policy, select Show advanced 
options, and then enter details for the storage location as described in the following table.
18 When you are satisfied with the repository configuration information you entered, click Next.
The Encryption page appears.
19 Optionally, to enable encryption, on the Encryption page, select Enable Encryption.
CAUTION: If you delete your repository in the future, the Installer program will remove the entire 
contents of the repository path. For this reason, do not create the storage location at the root (for 
example, c:\), which could result in losing all data stored on that volume.
NOTE: If the storage location is a New Technology File System (NTFS) volume using Windows XP or 
Windows 7, the file size limit is 16 TB.

If the storage location is a NTFS volume using Windows 8, 8.1 or Windows Server 2012, 2012 R2, the 
file size limit is 256 TB.

For AppAssure to validate the storage location, Windows Management Instrumentation (WMI) must 
be installed and accessible on the operating system hosting the AppAssure Core.
Table 52. Advanced options for storage
Te x t  B o x D e s c r i p t i o n
Bytes per Sector Specify the number of bytes you want each sector to include. The 
default value is 512.
Bytes per Record Specify the average number of bytes per record. The default value is 
8192.
Write Caching Policy The write caching policy controls how the Windows Cache Manager is 
used in the repository and helps to tune the repository for optimal 
performance on different configurations.
Set the value to one of the following:
•On
•Off
•Sync
If set to On, which is the default, Windows controls the caching.
NOTE: Setting the write caching policy to On could result in faster 
performance. If you are using a version of Windows Server prior to Server 
2012, the recommended setting is Off.
If set to Off, AppAssure controls the caching.
If set to Sync, Windows controls the caching as well as the synchronous 
input/output. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B111 Encryption key fields appear on the Encryption page.
20 If you want to encrypt this protected machine using an encryption key that is already defined on this 
AppAssure Core, select Encrypt data using an existing Encryption key, and select the appropriate key 
from the drop-down menu.
Proceed to Step 22.
21 If you want to add a new encryption key to the Core and apply that key to this protected machine, then 
enter the information as described in the following table.
22 Click Finish to save and apply your settings.
The first time protection is added for a machine, a base image (that is, a snapshot of all the data in the 
protected volumes) will transfer to the repository on the AppAssure Core following the schedule you 
defined, unless you specified to initially pause protection.
Creating custom protection schedules
When defining protection using the Protect a Machine Wizard or the Protecting Multiple Machines Wizard, you 
must define a protection schedule.
The default protection schedule includes a single period that includes each day of the week. The default time 
range is from 12:00 AM to 11:59 PM, covering a full 24-hour time period. The default interval is 60 minutes.
Using the wizard, you can customize protection schedules, choosing either periods or a daily protection time.
Selecting periods allows you to view the default protection schedule and make adjustments accordingly. 
Selecting a daily protection time causes AppAssure to back up the designated protected machines once daily at 
a time you specify.
NOTE: If you enable encryption, it will be applied to data for all protected volumes for this agent 
machine.

You can change the settings later from the Configuration tab in the AppAssure Core Console.

For more information about encryption, see the topic Understanding encryption keys.
CAUTION: AppAssure uses AES 256-bit encryption in the Cipher Block Chaining (CBC) mode with 256-
bit keys. While using encryption is optional, Dell highly recommends that you establish an encryption 
key, and that you protect the passphrase you define. Store the passphrase in a secure location as it is 
critical for data recovery. Without a passphrase, data recovery is not possible.
Table 53. Encryption key settings
Te x t  B o x D e s c r i p t i o n
Name Enter a name for the encryption key.
Encryption key names must contain between 1 and 130 alphanumeric 
characters. You may not include special characters such as the back slash, 
forward slash, pipe, colon, asterisk, quotation mark, question mark, open or 
close brackets, ampersand or hash.
Description Enter a comment for the encryption key.
This information appears in the Description field when viewing encryption 
keys from the Core Console.
Passphrase Enter the passphrase used to control access.
Best practice is to avoid special characters listed above.
Record the passphrase in a secure location. Dell Support cannot recover a 
passphrase. Once you create an encryption key and apply it to one or more 
protected machines, you cannot recover data if you lose the passphrase.
Confirm Passphrase Re-enter the passphrase you just entered. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B112 When using periods, you can make simple changes to the default protection schedule. For example, you may 
want to simply change the interval in the default weekday schedule to every 20 minutes, resulting in backups 
three times hourly instead of once hourly, or every 180 minutes, resulting in backups once every three hours.
You can also create more complex protection schedules. For example, you can create peak periods for 
weekdays, and off-peak periods for weekends, as described in Understanding protection schedules.
Finally, when protecting one or multiple machines using the wizard, you can initially pause protection, which 
defines the protection schedule without starting protection. When you are ready to begin protecting your 
machines based on the established protection schedule, you must explicitly resume protection. For more 
information on resuming protection, see Pausing and resuming protection. Optionally, if you want to protect a 
machine immediately, you can force a snapshot. For more information, see Forcing a snapshot.
Complete the steps in this procedure to create custom schedules for protecting data on agent machines when 
defining protection using a wizard.
To create custom schedules
1 On the Protection Schedule page of the Protect Machine or Protect Multiple Machines Wizard, to change 
the interval schedule for any period, do the following:
aSelect Periods.
The existing periods display and can be modified. Editable fields include a start time, end time, 
and interval (in minutes) for each period.
b Click in the interval field and type an appropriate interval in minutes.
For example, highlight the existing interval and replace it with the value 20 to perform snapshots 
every 20 minutes in this period.
2 To create a peak and off-peak period for weekdays, change the time range of the weekday period so that 
it does not include a 24-hour period, set an optimal interval for the peak, select Take snapshots for the 
remaining time and set an off-peak interval, by doing the following:
aSelect Periods.
The existing periods display and can be modified.
bClick in the From box to change the start time for this period.
The Choose Time dialog box appears.
c Drag the Hours and Minutes slider controls as appropriate for the desired start time, and then 
click Done. To specify the current time, click Now.
For example, drag the Hours control to show a time of 08:00 AM
dClick in the To box to change the end time for this period.
The Choose Time dialog box appears.
e Drag the Hours and Minutes slider controls as appropriate for the desired start time, and then 
click Done. To specify the current time, click Now.
For example, drag the Hours control to show a time of 04:59 PM
3 To set a single time of day for a single backup to occur daily, select Daily protection time and then enter 
a time in format HH:MM AM. For example, to do a daily backup at 9:00 PM, enter 09:00 PM.
NOTE: For conceptual information about protection schedules, see Understanding protection schedules. 
For information about protecting a single machine, see Protecting a machine. For information about bulk 
protect (protecting multiple machines), see Protecting multiple machines. For information on customizing 
protection periods when protecting an agent using either of these wizards, see Creating custom protection 
schedules. For information about modifying an existing protection schedule, see Modifying protection 
schedules. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B113 4 To define the schedule without beginning backups, select Initially pause protection.
After you pause protection from the wizard, it remains paused until you explicitly resume it. Once you 
resume protection, backups will occur based on the schedule you established. Fore more information on 
resuming protection, see Pausing and resuming protection.
5 When you are satisfied with changes made to your protection schedule, click Finish or Next, as 
appropriate. Return to the procedure for the appropriate wizard to complete any requirements 
remaining.
Modifying protection schedules
A protection schedule defines when backups are transferred from protected agent machines to the AppAssure 
Core. Protection schedules are initially defined using the Protect Machine Wizard or the Protect Multiple 
Machines Wizard.
You can modify an existing protection schedule at any time from the Summary tab for a specific agent machine.
Complete the steps in this procedure to modify an existing protection schedule for volumes on a protected 
machine.
To modify protection schedules
1 Navigate to the AppAssure Core Console.
2 From the list of protected machines, select the machine with a defined protection schedule that you 
want to change.
The Summary tab displays for the machine.
3 Select the volumes for the protected machine that you want to change, and click Set a schedule. To 
select all volumes at once, click in the checkbox in the header row.
Initially, all volumes share the same protection schedule. Typically, it is good practice to protect, at 
minimum, the System Reserved volume and the volume with the operating system (typically the C drive).
The Protection Schedule dialog box appears.
4 On the Protection Schedule dialog box, if you previously created a protection schedule template and 
want to apply it to this agent, select the template from the drop-down list, and then go to Step 10.
5 If you want to save this new protection schedule as a template, enter a name for the template in the 
text box.
6 If you want to remove an existing time period from the schedule, clear the check boxes next to each 
time period option. Options include the following:
•Mon - Fri. This range of time denotes a typical five-day work week.
•Sat - Sun. This range of time denotes a typical weekend.
7 If the weekday start and end times are from 12:00 AM to 11:59 PM, then a single period exists. To change 
the start or end time of a defined period, do the following:
a Select the appropriate time period.
bClick in the Start Time box to change the start time for this period.
The Choose Time dialog box appears.
NOTE: For conceptual information about protection schedules, see Understanding protection schedules. 
For information about protecting a single machine, see Protecting a machine. For information about bulk 
protect (protecting multiple machines), see Protecting multiple machines. For information on customizing 
protection periods when protecting an agent using either of these wizards, see Creating custom protection 
schedules. For information about modifying an existing protection schedule, see Modifying protection 
schedules. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B114 c Drag the Hours and Minutes slider controls as appropriate for the desired start time, and then 
click Done. To specify the current time, click Now.
For example, drag the Hours control to show a time of 08:00 AM
dClick in the End Time box to change the end time for this period.
The Choose Time dialog box appears.
e Drag the Hours and Minutes slider controls as appropriate for the desired start time, and then 
click Done. To specify the current time, click Now.
For example, drag the Hours control to show a time of 04:59 PM
f Change the interval according to your requirements. For example, if defining a peak period. 
change the interval from 60 minutes to 20 minutes to take snapshots three times hourly.
8 If you defined a period other than 12:00 AM to 11:59 PM in Step 7, then if you want backups to occur in 
the remaining time ranges, you must add additional periods to define protection by doing the following:
aClick + Add period.
Under the appropriate category (weekdays or weekends), a new time period appears. If the first 
period started later than 12:00 AM, then AppAssure automatically starts this period at 12:00. 
Following the above example, this second period starts at 12:00 AM. You may need to adjust hours 
or minutes for the start and end times.
b Drag the Hours and Minutes slider controls as appropriate for the desired start and end times, as 
appropriate.
For example, set a start time of 12:00 AM and an end time of 07:59 AM.
c Change the interval according to your requirements. For example, if defining an off-peak period. 
change the interval from 60 minutes to 120 minutes to take snapshots every two hours.
9 If needed, continue to create additional periods, setting start and end times and intervals as 
appropriate.
10 When your protection schedule meets your requirements, click Apply.
The protection Schedule dialog box closes.
Pausing and resuming protection
When you pause protection, you temporarily stop all transfers of data from the selected machine to the 
AppAssure Core. When you resume protection, the AppAssure Core follows the requirements in the protection 
schedule, backing up your data regularly based on that schedule.
You can pause protection for any AppAssure agent machine:
•When establishing protection using the Protect Machine Wizard or the Protect Multiple Machines Wizard.
•From the Protected Machines menu in the left navigation area of the AppAssure Core (pausing protection 
for all agents).
•From the Protected Machines page (accessible when you click on the Protected Machines menu).
•From a specific protected machine in the Protected Machines menu.
•From the Summary tab of any protected agent machine.
If you pause protection using the Protect Machine Wizard or the Protect Multiple Machines Wizard, protection is 
paused until explicitly resumed.
If you pause protection outside of a wizard, you can choose whether to pause protection until resumed, or to 
pause it for a designated amount of time (specified in any combination of days, hours and minutes). If you pause 
NOTE: If you want to remove a period you have added, click the X to the far right of that period. If 
you remove a period in error, you can click Cancel. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B115 for a period of time, then when that time expires, the system resumes protection based on the protection 
schedule automatically.
You can resume protection for any paused AppAssure agent:
•From the Protected Machines menu in the left navigation area of the AppAssure Core (resuming 
protection for all agents).
•From a specific protected machine in the Protected Machines menu.
•From the Protected Machines page (accessible when you click on the Protected Machines menu).
•From the Summary tab of any protected agent machine.
Use the procedure below to pause or to resume protection, as appropriate.
To pause and resume protection
1 In the AppAssure Core Console, to pause or resume protection for all machines, click the Protected 
Machines drop-down menu in the left navigation area.
•If you want to pause protection, do the following:
aSelect Pause Protection.
The Pause Protection dialog box appears.
b Select the appropriate setting using one of the options described below, and then click 
OK.
•If you want to pause protection until you explicitly resume it, select Pause until 
resumed.
•If you want to pause protection for a specified period, select Pause f or and then, in 
the Days, Hours, and Minutes controls, type or select the appropriate pause period 
as appropriate.
•If you want to resume protection, do the following:
aSelect Resume Protection.
The Resume Protection dialog box appears.
b In the Resume Protection dialog box, select Ye s.
The Resume Protection dialog box closes, and protection is resumed for all machines.
2 To pause or resume protection for a single machine from any tab, then in the left navigation area, from 
the list of protected machines, click the arrow to the right of the machine you want to affect.
•If you want to pause protection, do the following:
aSelect Pause Protection.
The Pause Protection dialog box appears.
b Select the appropriate setting using one of the options described below, and then click 
OK.
•If you want to pause protection until you explicitly resume it, select Pause until 
resumed.
•If you want to pause protection for a specified period, select Pause f or and then, in 
the Days, Hours, and Minutes controls, type or select the appropriate pause period 
as appropriate.
•If you want to resume protection, do the following:
aSelect Resume Protection.
The Resume Protection dialog box appears. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B116 b In the Resume Protection dialog box, select Ye s.
The Resume Protection dialog box closes, and protection is resumed for the selected 
machine.
3 To pause or resume protection for a single machine from the Summary tab, navigate to the machine that 
you want to affect.
The Summary tab displays for the selected machine appears.
•If you want to pause protection, do the following:
aIn the Actions drop-down menu for that machine, select Pause Protection.
The Pause Protection dialog box appears.
b Select the appropriate setting using one of the options described below, and then click 
OK.
•If you want to pause protection until you explicitly resume it, select Pause until 
resumed.
•If you want to pause protection for a specified period, select Pause f or and then, in 
the Days, Hours, and Minutes controls, type or select the appropriate pause period 
as appropriate.
•If you want to resume protection, do the following:
aSelect Resume Protection.
The Resume Protection dialog box appears.
b In the Resume Protection dialog box, select Ye s.
The Resume Protection dialog box closes, and protection is resumed for the selected 
machine.
Protecting multiple machines
You can add two or more Windows machines for protection on the AppAssure Core simultaneously using the 
Protect Multiple Machines Wizard. This feature is called bulk protection.
As with protecting individual machines, bulk protection requires the AppAssure Agent software to be installed 
on each machine you want to protect, and requires that machine to be restarted after installation of the Agent 
software. There is more than one method to deploy the Agent software to multiple machines simultaneously. 
For example:
•You can install the AppAssure Agent software to multiple machines using the bulk deploy feature, 
accessed from the Tools tab. (If you selected Protect Machine After Install when you deployed the 
Agent, you can skip this procedure.) For more information about using bulk deploy, see Deploying to 
multiple machines.
•You can deploy the AppAssure Agent software as part of this wizard.
This process includes optional steps you can access if you select an advanced configuration. Advanced options 
include repository functions and encryption. For example, you can specify an existing AppAssure repository to 
save snapshots, or create a new repository. You can also specify an existing encryption key (or add a new 
encryption key) to apply to the data saved to the Core for this machine.
The workflow of the Protect Multiple Machines Wizard may differ slightly based on your environment. For 
example, if the AppAssure Agent software is installed on the machines you want to protect, you will not be 
prompted to install it from the wizard. Likewise, if a repository already exists on the Core, you will not be 
prompted to create one.
NOTE: Protected machines must be configured with a security policy that makes remote installation 
possible. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B117
To protect multiple machines
1 If you have already installed the AppAssure Agent software on the machines you want to protect, but 
have not restarted them yet, restart the machines now.
2 On the Core machine, navigate to the AppAssure Core Console, click the drop-down menu next to the 
Pr ote ct  ico n ,  an d  se le ct Bulk Protect.
The Protect Multiple Machines Wizard appears.
3 On the Welcome page, select the appropriate installation options:
•If you do not need to define a repository or establish encryption, select Ty p i c a l.
•If you need to create a repository, or define a different repository for backups for the selected 
machines, or if you want to establish encryption using the wizard, select Advanced (show 
optional steps).
•Optionally, if you do not wish to see the Welcome page for the Protect Machine Wizard in the 
future, select the Skip this Welcome page the next time the wizard opens option.
4 When you are satisfied with your choices on the Welcome page, then click Next.
The Connection page appears.
5 Select the appropriate method to identify the machines you want to add for protection.
The machines must be on and accessible in order to connect to them. For successful connection using 
Active Directory, bulk protection and bulk deploy will be most successful if logged into the machines as 
the domain administrator.
•To identify the machines you want to protect on an Active Directory domain, select Connect to 
Active Directory, enter credentials as described in the following table, and then click Next. Skip 
to Step 7.
•To identify the machines you want to protect on a VMware vCenter/ESX(i) virtual host, select 
Connect to vCenter/ESX(i), enter credentials as described in the following table, and then click 
Next. Skip to Step 7.
•To add the machines manually, select Add the machines manually and then click Next.
The Machines page appears.
6 On the Machines page, to specify machines manually, type the connection details for each machine on a 
separate line, and then click Next. Use the following format:
hostname::username::password::port Table 54. vCenter/ESX(i) credentials
Te x t  B o x D e s c r i p t i o n
Host The host name or IP address of the Active Directory domain or of the VMware vCenter 
Server/ESX(i) virtual host.
User name The user name used to connect to the domain: for example, Administrator or, if the 
machine is in a domain, [domain name]\Administrator).
Password The secure password used to connect to the domain.
NOTE: All virtual machines must have VM Tools installed; otherwise, AppAssure cannot 
detect the host name of the virtual machine to which to deploy the Agent software, and 
cannot protect that machine. In lieu of the host name, AppAssure uses the virtual machine 
name, which may cause issues if the host name is different from the virtual machine name.
NOTE: The port parameter is optional; if omitted, port 8006 will be used by default. If you wish to 
specify a port different than 8006, then inclusion of this parameter is required. 
						

							Dell AppAssure User Guide
Version 5.4.3 Revision B118 7 On the Machines page, to specify machines identified from an Active Directory domain or from a VMware 
vCenter/ESX(i) virtual host, select each appropriate machine you want to protect from the list. Ensure 
you clear the checkbox option for any machine you do not want to protect at this time. When satisfied, 
then click Next.
The system verifies each machine you added automatically.
8 If the Protection page appears next in the Protect Multiple Machines Wizard, skip to Step 12.
If the Agent software is not yet deployed to the machines you want to protect, or if any of the machines 
you specified cannot be protected for another reason, then the selected machines appear on the 
Machines Warnings page. The system verifies each machine you added automatically.
9 Optionally, on the Machines Warnings page, you can verify any machine by selecting the machine and 
then clicking Ve r i f y in the toolbar.
10 Optionally, on the Machines Warnings page, select After Agent installation, restart the machines 
automatically.
11 If the status indicates that the machine is reachable, click Next to install the agent software.
The Protection page appears.
12 On the Protection page, select the appropriate protection schedule as described below.
•If you want to use the default protection schedule, then in the Schedule Settings option, select 
Default protection (hourly snapshots of all volumes).
•If you want to define a different protection schedule, then in the Schedule Settings option, select 
Custom protection and then click Next.
13 Proceed with your configuration as follows:
•If you selected a Typical configuration for the Protect Multiple Machines Wizard, and default 
protection, then click Finish to confirm your choices, close the wizard, and protect the machines 
you specified.
•If you selected a Typical configuration for the Protect Multiple Machines Wizard and specified 
custom protection, then on the Protection page, click Next, and on the Protection Schedule page, 
set up a custom schedule as described in the topic Creating custom protection schedules, and 
then click Finish to confirm your choices, close the wizard, and protect the machines you 
specified.
•If you selected Advanced configuration for the Protect Machine Wizard, then click Next and 
proceed to Step 14 to see repository and encryption options.
14 On the Repository page, if you want to store the data for all of the machines you specified for protection 
in an existing repository, then select Use an existing repository, select the appropriate repository from 
the list, and then click Next and proceed to Step 19.
If you want to create a new storage location on the Core, then do the following:
aSelect Create a Repository.
b On the Repository page, in the Name field, specify the name of the repository you want to 
create.
This is typically the word Repository and an index number, which corresponds to the number of 
the new repository (for example, Repository1). You can change the name as needed. You can 
enter up to 40 characters. This name must be unique for this core.
NOTE: Dell recommends this option. You must restart agent machines before they can be 
protected.
NOTE: When specifying the repository name, use only alphanumeric characters or the 
hyphen. No other symbols or punctuation characters are permitted. Do not use letter 
combinations that specify commands or reserved words (such as con, prn, aux or nul) or 
that represent ports (such as com or lpt).