HP StoreOnce D2D4324 HP StoreOnce Backup System Concepts and Configuration Gui - Page 73

Backup file size, to Disk Folder, or even Virtual Tape Library.

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When using a backup application with StoreOnce NAS shares the user will need to configure a new type of device in their backup application. Each application varies as to what it calls a backup device that is located on a StoreOnce device, for example it may be called a File Library, Backup to Disk Folder, or even Virtual Tape Library. Most backup applications allow the operator to set various parameters related to the NAS backup device that is created, these parameters are important in ensuring good performance in different backup configurations. Generic best practices can be applied to all applications as follows. Backup file size Backup applications using disk/NAS targets will create one or more large backup files per backup stream; these contain all of the backed up data. Generally a limit will be set on the size that this file can get to before a new one is created (usually defaulting to 4-5 GB). A backup file is analogous to a virtual cartridge for VTL devices, but default file sizes will be much smaller than a virtual cartridge size (e.g. a virtual cartridge may be 800 GB). In addition to the data files, there will also be a small number of metadata files such as catalogue and lock files, these will generally be smaller than the 24 MB dedupe threshold size and will not be deduplicated. These files are frequently updated throughout the backup process, so allowing them to be accessed randomly without deduplication ensures that they can be accessed quickly. The first 24 MB of any backup file will not be deduplicated, with metadata files this means that the whole file will not be deduplicated, with the backup file the first 24 MB only will not be deduplicated. This architecture is completely invisible to the backup application which is merely presented with its files in the same way as any ordinary NAS share would do so. It is possible that the backup application will modify data within the deduplicated data region; this is referred to as a write-in-place operation. This is expected to occur rarely with standard backup applications because these generally perform stream backups and either create a new file or append to the end of an existing file rather than accessing a file in the middle. If a write-in-place operation does occur, the StoreOnce appliance will create a new backup item that is not deduplicated, a pointer to this new item is then created so that when the file is read the new write-in-place item will be accessed instead of the original data within the backup file. If a backup application were to perform a large amount of write-in-place operations, there would be an impact on backup performance - because of the random access nature that write in place creates. Some backup applications provide the ability to perform "Synthetic Full" backups, these may produce a lot of write-in-place operations or open a large number of files all at once, it is therefore recommended that Synthetic Full backup techniques are not used. Generally configuring larger backup container file sizes will improve backup performance and deduplication ratio because: 1. The overhead of the 24 MB dedupe region is reduced. 2. The backup application can stream data for longer without having to close and create new files. 3. There is a lower percentage overhead of control data within the file that the backup application uses to manage its data files. 4. There is no penalty to using larger backup files as disk space is not usually pre-allocated by the backup application. If possible the best practice is to configure a container file size that is larger than the complete backup will be (allowing for some data growth over time), so that only one file is used for each backup. Some applications will limit the maximum size to something smaller than that however, in which case, using the largest configurable size is the best approach. Backup application configuration 73

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When using a backup application with StoreOnce NAS shares the user will need to configure a
new type of device in their backup application. Each application varies as to what it calls a backup
device that is located on a StoreOnce device, for example it may be called a File Library, Backup
to Disk Folder, or even Virtual Tape Library.
Most backup applications allow the operator to set various parameters related to the NAS backup
device that is created, these parameters are important in ensuring good performance in different
backup configurations. Generic best practices can be applied to all applications as follows.
Backup file size
Backup applications using disk/NAS targets will create one or more large backup files per backup
stream; these contain all of the backed up data. Generally a limit will be set on the size that this
file can get to before a new one is created (usually defaulting to 4–5 GB). A backup file is analogous
to a virtual cartridge for VTL devices, but default file sizes will be much smaller than a virtual
cartridge size (e.g. a virtual cartridge may be 800 GB).
In addition to the data files, there will also be a small number of metadata files such as catalogue
and lock files, these will generally be smaller than the 24 MB dedupe threshold size and will not
be deduplicated. These files are frequently updated throughout the backup process, so allowing
them to be accessed randomly without deduplication ensures that they can be accessed quickly.
The first 24 MB of any backup file will not be deduplicated, with metadata files this means that
the whole file will not be deduplicated, with the backup file the first 24 MB only will not be
deduplicated. This architecture is completely invisible to the backup application which is merely
presented with its files in the same way as any ordinary NAS share would do so.
It is possible that the backup application will modify data within the deduplicated data region; this
is referred to as a write-in-place operation. This is expected to occur rarely with standard backup
applications because these generally perform stream backups and either create a new file or
append to the end of an existing file rather than accessing a file in the middle.
If a write-in-place operation does occur, the StoreOnce appliance will create a new backup item
that is not deduplicated, a pointer to this new item is then created so that when the file is read the
new write-in-place item will be accessed instead of the original data within the backup file.
If a backup application were to perform a large amount of write-in-place operations, there would
be an impact on backup performance – because of the random access nature that write in place
creates.
Some backup applications provide the ability to perform “Synthetic Full” backups, these may
produce a lot of write-in-place operations or open a large number of files all at once, it is therefore
recommended that Synthetic Full backup techniques are not used.
Generally configuring larger backup container file sizes will improve backup performance and
deduplication ratio because:
1.
The overhead of the 24 MB dedupe region is reduced.
2.
The backup application can stream data for longer without having to close and create new
files.
3.
There is a lower percentage overhead of control data within the file that the backup application
uses to manage its data files.
4.
There is no penalty to using larger backup files as disk space is not usually pre-allocated by
the backup application.
If possible the best practice is to configure a container file size that is larger than the complete
backup will be (allowing for some data growth over time), so that only one file is used for each
backup. Some applications will limit the maximum size to something smaller than that however,
in which case, using the largest configurable size is the best approach.
Backup application configuration
73