Archive:The DataStore 4.0

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DataStores

Until now media types for disk backups (DiskHard and DiskChange) were based on the historic media concept of tape backups. This means a media pool based on these media types has to be separated into logical media.

From Sesam version 4.0.3.x disk backups should be save to the Sesam DataStore. With it the defined disks (partitions) are managed as a whole. Using Sesam DataStore provide several new functions and features.

DataStore features

  • SEP sesam still backs primary up to a mediapool. Now Backup to disk based on one or several Sesam DataStores.
  • A DataStore doesn't have a traditional media structure. Data will be written in dynamically managed data areas.
  • When a backup writes a DataStore full the saveset will not splitted. In this case the backup breaks. This behavior you have to regard during the planning of DataStore dimensioning (see Using recommendations).
  • The lock time (EOL) will still defined on the mediapool. On backup onto a DataStore these lock times are valid on the backup saveset directly not on a medium or data area anymore. This means only the space for the saveset will be locked on disk.
  • DataStore space will be managed on partition level, means the determination of the fill rate on filesystem level is too time-consuming and on big partition not useful presentable.
  • During DataStore configuration all values (capacity and watermarks) will specified by negative values. These values define the space which should be free on DataStore (partition).
  • When you set up the low watermark (LWM) less than zero (LWM<0) a saveset hold-back time longer than the requested off-time (EOL) can be reached. For that the DataStore has to calculate big enough.
  • A DataStore purge process will be triggered by different events.
  • On using a mediapool with more than one DataStores the backups will dynamically and evenly distributed by Sesam queue manager (balancing).
  • With the high watermark (HWM) and low watermark (LWM) the DataStore saturation can be optimized.
  • If HWM cannot be undershot during a purge process an event will be triggered by SEP sesam alarm interface. By default an email will be sent when the Sesam alarm interface is activated and email notification on SEP sesam server is configured.

Using recommendations

  • DataStore volume sizing and occupancy will be managed on partition level. You shouldn't store no other data than the Sesam backup data.
  • The DataStore should have the triple maximum full backup size of the planned backups hence the watermarks can work automatically and dynamically.
  • It could be possibly necessary to scale the DataStore bigger than three times of the max size when a longer hold-back time is stipulated or very big saveset will be stored.
  • The design should run in the direction, that ...
    • ... between Capacity and HWM a complete full backup should have enough space.
    • ... an another full backup should have space between HWM and LWM.
    • ... a third full inside the LWM area.
  • A virtual drive can handle up to 124 simultaneous backups (channels) to store the data onto a Sesam DataStore (depends on SEP sesam version). When it's necessary to backup more than these channels (possible from SEP sesam server premium edition) only then you should add an another drive to the DataStore.
  • Because a backup which filled the DataStore completely won't be split but the backup will break you make sure how the propotion between the DataStore size and the size of the biggest backup task. E.g. a DataStore will defined with 3 TB whereas the biggest saveset is already 2 TB, then with an EOL=1 a triple DataStore size can even to small to allow the watermarks work properly. In this case it could recommended that the DataStore size should designed bigger.

Restrictions

  • When a mediapool should use more than one Datastore, all DataStores have to connect to the same Sesam Device Server (IP host). An operation with one mediapool serves network ditributed DataStores will currently not sopprted.

Function

In a classic media pool based on DiskHard the directory of the storage space is defined in the media pool.


DataStore Principle 403b.jpg


With DataStore this definition happens on the drive. As shown in the illustration, a media pool still points to a drive group. Only now one or more DataStores are set in between as an additional level. The connection of a DataStore to the drive is static.

Several DataStores are only needed in a media pool if a media pool is supposed to use the data of several disk partitions. In this case all drives of the DataStores of a mediapool must be part of the same drive group. This ensures that the SEP sesam queue manager can distribute the backups on this media pool on all DataStores (Balancing).

The disk space usage management of the DataStore only uses operating system functions of partitions. This means that several DataStores can be set up on a partition, however every DataStore sees the values of the other partitions when checking the partition allocation. This means that the DataStores obstruct each other. It is therefore recommended that you only use one DataStore for each hard disk partition.

Watermarks and Purge

So-called watermarks are available for managing the disk space usage. The High Watermark (HWM) defines how full a DataStore can get until a Purge deletes obsolete files (EOL free). The Low Watermark (LWM) defines how much of the EOL-free files can be deleted from the DataStore. If a LWM=0 is set, all EOL-free savesets are physically removed from the DataStore regardless the filler loading. This value can be used to control how much storage space is made available for files with expired EOLs in the DataStore. This way a data history that exceeds a necessary minimum can be provided on disk. SEP sesam always deletes the oldest savesets first.


DataStore Watermarks-Purge 403b.jpg


Events that lead to a Purge in a DataStore:

  • New day
  • After sharing the drive of the DataStore after a backup
  • Manual Purge in the GUI

Instructions

I. How to set up a DataStore

II. How to use a DataStore

III. How to administer a DataStore

IV. How to maintain a DataStore


DataStore GUI-View 403en.jpg


The column value of the Sesam DataStore table contain following values:

Capacity
The partition size added this value the sesam use the result size of the partition for backups.
Filled
How much data the Sesam has already written.
High Water Mark
High watermark treshold
Low Water Mark
Low watermark treshold
Total
Partition capacity where the Sesam DataStore stores its data. This Size is the result of a operating system request.
Used
So much data occupy space on that partition. (Not only the Sesam data - what the Sesam stored, see the column filled).
Free
Free size of the partition on which the Sesam DataStore is configured.