The DataStore 4.4

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Data stores

A data store is a device type used for writing the save sets directly on one or several configured storage locations – into the file system. Data store configuration consists of specifying data store capacity and watermarks: HWM and LWM.

The default data store type is Path. This data store type is relevant for configuring all storage locations, except for SEP sesam additional archiving and deduplication module that uses a dedicated SEP Si3 deduplication store. As of SEP sesam version 4.4.3, SEP EasyArchive data store and FDS deduplication store are no longer supported.

SEP sesam uses a data store instead of a conventional media pool to define storage repository. The data is still primarily backed up to a media pool, however a data store is used underneath to save data to dynamically managed data areas, including disk backups.

Data store concept

The difference beween a conventional media pool, typically used for backing up directly to tapes, and a data store is in defining the storage space directory directly in the drive by using the operating system's partition functions. Therefore the data store space is managed at partition level.

Another difference is that when a data store becomes full during backup, the save set will not be split up. Instead, the backup will be aborted. You should consider this when specifying the data store capacity. For details, see Data store calculation recommendations below.

Information sign.png Note
Only one data store should be used for each hard disk partition. Even though several data stores can be set up on one partition, you are advised against such configuration as each data store reads the values of the other partitions when checking partition allocation. Consequently, such coexisting data stores obstruct each other.

As shown in the illustration below, a media pool still points to a drive group. However, there is now an additional level of one or more data stores between the media pool and the drives. The connection between a data store and the related drive is static.

DataStore Principle 403b.jpg


Data store capacity

Data store configuration consists of specifying the data store capacity and watermarks. The data store capacity is space reserved for the SEP sesam data store and, optionally, non-SEP sesam data that might be stored on the same volume as the SEP sesam data store. If the data store is shared with non-SEP sesam data, you will have to obtain a special SEP sesam storage license.

When specifying the capacity value, a dedicated partition must have enough free space. From SEP sesam version 4.4 onwards, the method for calculating the required disk space is:
space occupied by Sesam + free disk space = DS capacity

where DS capacity is the configured capacity value in SEP sesam's data store configuration. For examples on calculating a data store capacity, see How do I calculate the data store capacity.

More than one data store is required in a media pool only if the media pool uses data from several disk partitions, in which case all the drives of a media pool's data stores must be part of the same drive group. This ensures that the SEP sesam queue manager distributes the backups in this media pool to all data stores (balancing). For details on drive groups, see Drives.

Watermarks and purge

A watermark is a parameter used for data store configuration (managing disk space usage).

  • A high watermark (HWM) is the upper value for the used disk space on the data store. It defines the available storage space for backup and migration. When this value is reached, a data store purge process is started for all obsolete (EOL-free) save sets.

The oldest free save sets are deleted first. Purging is done until the low watermark is reached. When setting the HWM parameter, you should ensure that sufficient space is allocated between data store capacity and HWM for a complete full backup. Otherwise the backup will be canceled (file system full). For details, see Data store calculation recommendations below.

  • A low watermark (LWM) is the lower value for the used disk space on the data store. It defines how much storage space is available for save sets with expired EOL and how many EOL-free files can be deleted from the data store. If LWM is set to 0 (default value), all EOL-free save sets are removed from the data store, regardless the filler loading. If both watermarks, HWM and LWM are used, all EOL-free savesets will only be purged, when the HWM is exceeded.
DataStore Watermarks-Purge 403b.jpg


Events that trigger the data store purge are:

  • NEWDAY
  • Sharing the drive of the data store after a backup
  • Starting purge manually in GUI

Data store calculation recommendations

  • Data store volume sizing and capacity usage should be managed at partition level. It is recommended that only SEP sesam data is stored on the respective volume.
  • The data store should be at least three times (3x) the maximum full backup size of the planned backup to allow the watermarks to work automatically and dynamically.
  • It may be necessary to scale up the data store to beyond 3x the maximum size when a longer hold-back time is stipulated or very big save sets are to be stored. To do this, sufficient space should be allocated:
    • between capacity and HWM for a complete full backup
    • between HWM and LWM for another full backup
    • inside the LWM area for a third full backup
  • A virtual drive can handle up to 124 simultaneous backups (channels) for storing data to a SEP sesam data store (depending on the SEP sesam version). Only when it becomes necessary to back up more than 124 channels (SEP sesam server Premium Edition) should another drive be added to the data store.
  • Because a backup is terminated rather than split up when a data store becomes full, the correlation between the size of the data store and the size of the biggest backup task must be determined carefully. Take the example of a data store defined at 3 TB, whereas the biggest save set is 2 TB. With an EOL=1, a data store three times (3x) the maximum full backup size may be too small to allow the watermarks to work properly. In such a case, it is recommended to scale up the data store size.

Limitations

  • When a media pool requires more than one data store, all the data stores must be connected to the same SEP sesam Device Server (IP host). SEP sesam does not currently support network-distributed data stores being served by a single media pool.
  • When using more than one data store, only negative OR positive values can be used for capacity and HWM/LWM. SEP sesam does not support the use of negative AND positive values at the same time.

Instructions

I. How to set up a data store

II. How to use a data store

III. How to administer a data store

IV. How to maintain a data store

V. How to delete a data store

DataStore overview.png


Data store properties

The following are the properties of a data store:

Capacity
The size (in GB) of the partition available for backups.
Filled
The size (in GB) of the occupied data store space by SEP sesam.
High Water Mark
HWM treshold – the upper value (in GB) for the used disk space. When this value is reached, a purge process is triggered for all EOL-free save sets thus freeing up data store capacity.
Low Water Mark
LWM treshold – the value (in GB) for how much storage space is available for files with expired EOL in the data store. If LWM is set to 0 (default value), all EOL-free savesets are removed. For the deduplication store the LWM is not editable. It is set to 0 by default.
Total
Maximum available space (in GB) on the partition as reported by the operating system.
Used
Total used space (in GB) on the partition.
Free
Available disk space (in GB) for SEP sesam.

Save sets properties

Data store savesets.png


Selecting a data store and clicking the tab Savesets opens a list of all save sets with their details. You can change EOL of individual save set, adjust backup-related EOL, and lock or unlock individual save set.

Saveset EOL
The column Saveset EOL enables you to change EOL for each individual save set, stored on the respective data store. You can extend or reduce its retention time. If the adjusted save set is a part of a backup chain, the whole chain is affected. See EOL-related backup chain dependencies.
Backup EOL
The column Backup EOL enables you to adjust EOL for all save sets containing the same data. This backup-related EOL is applied to all save sets with the same data, including migrated and replicated save sets.
For example, adjusting EOL of a migrated save set from 2.12.2016 to 12.12.2017 results in changed EOL for all related backup data, i.e., original backup, replicated backup, as well as for all backups in a backup chain, if a save set with adjusted EOL is a part of it.
EOL-related backup chain dependencies
You can extend or reduce the retention period for an individual save set or backup-related save set, as described above. Keep in mind that increasing EOL of a DIFF or INCR save set will result in increased EOL of all dependent backups (FULL and other DIFF and INCR) in order to retain the backup data. This keeps the backup chain readily available for restore. On the other hand, decreasing the EOL of a DIFF or INCR save set to already passed time will result in a warning message prompting you to confirm your decision to set the whole backup chain to already passed time. By setting the expired EOL for DIFF or INCR save sets results in purging and overwriting the complete backup chain.
Information sign.png Note
Each save set can be re-used when the following conditions are met:
  1. Its EOL has expired.
  2. Typically, there must be no other save sets that depend on this save set. You can override this condition by explicitly allowing the EOL for the whole backup chain to be set to expired, thus deleting backup data on all related save sets.

See also

How to set up a data storeConfiguring an Si3 Deduplication Store