Best Practices for Backing Up Your System Luca Ravazzolo Technology Architect

Types of backups Cold file-level backup Caché online 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 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 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.

Advantages and Challenges

Caché online backup Advantages: Challenges: 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 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 There are two main types of storage snapshot, called the copy-on-write (or low-capacity) snapshot and the split-mirror snapshot. Utilities are available that can automatically generate either type. -A copy-on-write snapshot utility creates a snapshot of changes to stored data every time new data is entered or existing data is updated. This allows rapid recovery of data in case of a disk write error, corrupted file, or program malfunction. However, all previous snapshots must be available if complete archiving or recovery of all the data on a network or storage medium is needed. -A split-mirror snapshot utility references all the data on a set of mirrored drives. Every time the utility is run, a snapshot is created of the entire volume, not only of the new or updated data. This makes it possible to access data offline, and simplifies the process of recovering, duplicating, or archiving all the data on a drive. However, this is a slower process, and it requires more storage space for each snapshot. -- from http://searchstorage.techtarget.com/definition/storage-snapshot

CDP or replication Advantages Challenges 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 CDP = Continuous Data Protection

Coordinating with Caché External Backup Coordinating with Caché

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.log file.

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 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 #csession cache –U%SYS “##class(Backup.General).ExternalThaw()” #echo $? %SYS>SET rc=##class(Backup.General).ExternalThaw()

Another useful method Use Backup.General.ExternalSetHistory to log successful backups in the Backup History log is 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? 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_Operate and %Service_Terminal

Case Study: External Backup Using snapshots, a de-duplication appliance and replication for an external backup of Caché

External backup 1: Caché & snaps Backup software initiates the backup process from media server MEDIA Invoke script on server running Caché to FREEZE write daemon Backup software initiates clone or snapshot of all Caché arrays MEDIA Invoke script on server running Caché to THAW write daemon

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 Backup software initiates a backup copy to a secondary data center 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.

Timings and best practices Backup software initiates the backup process from media server MEDIA 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.

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 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 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 & copy Backup software mounts snapshot on the media server MEDIA Backup software does file level copy from snapshot to disk-based backup appliance. MEDIA 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.

Ext Backup 3: Replicate, verify & archive Backup software initiates a backup copy to a secondary data center MEDIA SAN level replication or replication via de- duplication appliance. Timings vary a lot here based on bandwidth and de-dupe rate if applicable.

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 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 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 Up Your System Luca Ravazzolo Technology Architect