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Best Practices for Backing U p Your System. Luca Ravazzolo Technology Architect. Types of backups. Cold file-level backup Caché shutdown Server-level copy to disk/tape Caché restarted Caché online backup Caché’s backup tool copies data blocks from CACHE.DAT files to disk file or tape.

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Best practices for backing u p your system

Best Practices for Backing Up Your System

Luca Ravazzolo

Technology Architect


Types of backups
Types of backups

  • Cold file-level backup

    • Caché shutdown

    • Server-level copy to disk/tape

    • Caché restarted

  • Caché online backup

    • Caché’s backup tool copies data blocks from CACHE.DAT files to disk file or tape.

    • Full or various incremental backups


Types of backups1
Types of backups

  • SAN or disk array backup

    • Backup I/O stays within the SAN or the array

    • Block level copy from device to device (disk, tape, virtual tape)

    • All vendors have some type of software to control backups.

    • To backup a consistent image, a point-in-time snapshot or clone is made of the source device.


Types of backups others
Types of backups: others

  • CDP: Continuous Data Protection (Near-CDP)

    • Use of separate appliance to journal changes out-of-band allowing for recovery to any point-in-time,

    • Depending on space available can restore to most any point-in-time.

  • SAN-based Replication

    • Provides a disk-to-disk copy within the SAN, perhaps over long distances,

    • Destination can be archived to tape.



Cach online backup
Caché online backup

  • Advantages:

    • Caché stays up, users continue to work

    • Simple to implement, may not need 3rd party software

  • Challenges:

    • Only backs up the CACHE.DAT data – must also backup journals, other files.

    • Restores typically take multiple steps

      • Create a Caché instance

      • Restore “*<date>.cbk” files from storage

      • Apply most recent full backup, then cumulative & incrementals

      • Apply journal files


Disk array san based snapshot
Disk array/SAN-based snapshot

  • Advantages:

    • Point-in-time copy of all data (Caché and otherwise)

    • Requires no downtime (when using Caché write daemon freeze and thaw)

  • Challenges:

    • Requires snap/clone technology

    • Requires additional software to coordinate


Cdp or replication
CDP or replication

  • Advantages

    • CDP allows restore to nearly any point-in-time

    • Replication allows geographically separated backups

  • Challenges

    • Non-Caché technologies require coordination with Caché, i.e.

      • May end up with Caché in a crash-consistent state and require recovery before use

    • Requires appliances and software


External backup

External Backup

Coordinating with Caché


Freeze the write daemon s
Freeze the write daemon(s)

  • For a consistent database image on your backup media (i.e. a CACHE.DAT without integrity errors) the write daemon’s cycle must be complete.

  • Use the Backup.General.ExternalFreeze() method

    • Keeps write daemon from writing

    • Waits for current write daemon cycle (if active) to finish

    • Switches journal file

    • Logs information to the cconsole.logfile.


Freezing the write daemon
Freezing the write daemon

  • ExternalFreeze command:

  • OS command returns a code:

    • 5 – successful

    • 3 - failure

  • While frozen, all updates are made as usual to database cache

  • Processes continue to run normally UNLESS:

    • Available buffers in the database cache falls too low.

    • The ExternalFreeze lasts longer than the default limit (600 seconds)

#csession cache –U%SYS “##class(Backup.General).ExternalFreeze()”

#echo $?

%SYS>SET rc=##class(Backup.General).ExternalFreeze()


Thaw the write daemon
Thaw the write daemon

  • Use Backup.General.ExternalThaw to allow write daemon(s) to resume writing.

  • Thaw command:

  • OS-level command returns one of these codes:

    • 5 – success

    • 3 - failure

%SYS>SET rc=##class(Backup.General).ExternalThaw()

#csession cache –U%SYS “##class(Backup.General).ExternalThaw()”

#echo $?


Another useful method
Another useful method

  • Use Backup.General.ExternalSetHistory to log successful backups in the Backup History

    • logis name of an externally created backup log

    • desc is free text

%SYS>SET log=“/var/logs/backup.log”,desc=“Full Backup”

%SYS>S rc=##class(Backup.General).ExternalSetHistory(log,desc)


Who runs the freeze thaw
Who runs the freeze/thaw?

  • The operating system user that executes the freeze/thaw command must have access to Caché.

    • In normal install, the “backup” user must be a Caché user.

    • %Service_Terminal must allow OS-level authentication.

    • Caché “backup” user needs RW on the %DB_CACHESYS resource as well as use of %Admin_Operateand %Service_Terminal


Case study external backup

Case Study: External Backup

Using snapshots, a de-duplication appliance and replication for an external backup of Caché


External backup 1 cach snaps
External backup 1: Caché & snaps

Backup software initiates the backup process from media server

MEDIA

Invoke script on server running Caché to THAW write daemon

Invoke script on server running Caché to FREEZE write daemon

Backup software initiates clone or snapshot of all Caché arrays

MEDIA


External backup 2 mount copy
External backup 2: Mount & copy

Backup software mounts snapshot on the media server

MEDIA

Backup software does file level copy from snapshot to disk-based backup appliance.

MEDIA

Backup releases the snapshot via command-line interface call to disk controller

MEDIA


Ext backup 3 replicate verify archive
Ext Backup 3: Replicate, verify & archive

MEDIA

In secondary data center, replicated backup is restored, mounted in a Caché instance and an integrity check is run to verify structural integrity.

Depending on space and policy backup is kept online and/or archived to tape for long term storage.

Backup software initiates a backup copy to a secondary data center


Timings and best practices
Timings and best practices

  • Backup software:

    • Must be able to call freeze/thaw script on Caché server

    • Must be able to initiate the snapshot

    • Most commercial backup software will work well including EMC Networker, Symantec NetBackup, IBM Tivoli (TSM), etc.

Backup software initiates the backup process from media server

MEDIA


Timings and best practices1
Timings and best practices

  • Sample scripts available from the WRC

  • Time to freeze and return depends on

    • Database activity

    • Current write daemon phase (i.e. is it writing to disk?)

Invoke script on server running Caché to FREEZE write daemon

04/02-02:30:00 (1098) 0 ExternalFreeze: Suspending system

04/02-02:30:00(1098) 0 ExternalFreeze: Description: Backup Performed by TSM at: 2013-04-02 02:30:00

04/02-02:30:01(1098) 0 ExernalFreeze: Start a journal restore for this backup

with journal file: /jrn/20130402.003

04/02-02:30:02(1098) 0 ExernalFreeze: System suspended


Timings and best practices2
Timings and best practices

  • Creating the clone or snap - this period is when write daemon(s) are frozen.

    • Timing is based on array controller activity

    • If greater than a few minutes there is a risk of running into freeze timeout.

50 seconds frozen with

IBM DS5300 using FlashCopy on

a few TB of data with active systems

Backup software initiates clone or snapshot of all Caché arrays

MEDIA

04/02-02:30:02(1098) 0 ExernalFreeze: System suspended

04/02-02:30:52 (9109) 0 ExternalThaw: Resuming system


Timings and best practices3
Timings and best practices

  • Thawing the write daemon takes seconds at most.

    • Best practice is to be sure to thaw the database on any error along the way.

    • Perhaps have an independent job to check database status and thaw if frozen---so a failed backup will never leave Caché frozen.

Invoke script on server running Caché to THAW write daemon


External backup 2 mount copy1
External backup 2: Mount & copy

  • Use of a de-duplication appliance as the file-level backup target speeds backup and saves space.

  • Timings vary a lot here---disk used, dedupe rate etc.

Backup software mounts snapshot on the media server

MEDIA

Backup software does file level copy from snapshot to disk-based backup appliance.

MEDIA


Ext backup 3 replicate verify archive1
Ext Backup 3: Replicate, verify & archive

  • SAN level replication or replication via de-duplication appliance.

  • Timings vary a lot here based on bandwidth and de-dupe rate if applicable.

MEDIA

Backup software initiates a backup copy to a secondary data center


Ext backup 3 replicate verify archive2
Ext Backup 3: Replicate, verify & archive

  • Integrity checks vary in timing

  • Another option is to have media server in primary data center run the check.

In secondary data center, replicated backup is restored, mounted in a Caché instance and an integrity check is run to verify structural integrity.

Depending on space and policy backup is kept online and/or archived to tape for long term storage.


Final points
Final points

  • Considering cost and effort, Caché online backup works well for small to medium size databases (~ 100s of GB total) with generous RTOs

  • Use InterSystems Mirroring in conjunction with your backup mechanism.

    • Perhaps there will be no need to restore a backup

    • If needed, the mirror destination will have CACHE.DAT files and journal files.


Final points1
Final points

  • Backup should have minimal impact on live database

  • Using SAN/disk controller based backups offloads the work to other appliances/servers

  • SAN/disk-based backups meet the fastest RTOs.

  • Restore from backup RPOs are as good as the most recently available journal file.


Best practices for backing u p your system1

Best Practices for Backing Up Your System

Luca Ravazzolo

Technology Architect


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