Disaster Recovery backups
joegard
certifies what IBM calls "Global mirroring" or Flashcopy for
DR sites. Basically, we have IBM storage. They have the
Global Mirroring on and we want to copy the database files
and any live updates to the hot site. I can't find anywhere
if it is certified. This would be in lieu of using the
Sybase Backup/Restore utilities.
Mark A. Parsons
engine capabilities.
I'd suggest contacting your Sybase sales rep, or opening a case with Sybase Tech Support, to see which (if any) IBM
storage options are certified with Sybase ASE.
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I haven't worked with IBM storage mirroring capabilities so fwiw ...
I've worked with several clients that have used Sybase ASE in conjunction with various EMC mirroring solutions; don't
recall which solutions are officially *certified* by Sybase but I do know that Sybase Tech Support never pushed back
with "that's not supported" when we opened various ASE-related cases.
The general idea is to use EMC's disk mirroring to keep a secondary ASE in sync with the primary ASE. While mirroring
is going on the secondary ASE has to be down and the 2 halves of the mirror have to be merged.
To split the mirror all activity must be suspended in the primary ASE (for all databases that reside on the disk
mirror(s) that's about to be split). Suspending primary ASE activity is usually handled in 1 of 2 ways ... 1) shutdown
the primary ASE or 2) use the 'quiesce database' command to halt ASE database activity.
While the mirror halves are merged (and secondary ASE is down), the mirroring can take place via synchronous or
asynchronous operations. Synchronous operations can be problematic if the mirror is located at the end of a
(relatively) 'slow' network connection ... primary issue is that primary ASE log writes are delayed while waiting for
the mirror copy to be written, the longer/slower the network connection the longer it takes to complete the primary
ASE's log write, thus the longer it takes for a spid to see a transaction to complete.
Some of my clients used the mirror to perform a 'fast' resync of the primary ASE; then the secondary ASE was used for
making backups, running reports and/or performing dbcc's.
"Duh, Mark!" ?
I would expect that if your IBM storage mirroring behaves the same as the EMC, then you should be able to use it with ASE.
Mark A. Parsons
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Assorted notes re: EMC mirroring features ...
If asynchronous mirroring is used to keep the mirrors in sync, you then have to take into consideration that the
secondary ASE is not guaranteed to be in sync (and may not actually be usable) in the case of your primary ASE and/or
EMC mirroring going down.
Obviously (?) if the mirror halves have been split then the two ASE dataservers cannot be kept in sync ... until the
mirror halves are re-merged. This means that you still need to perform database/log dumps from the primary ASE if you
need to be able to recover data modifications performed since the last database dump (ie, the secondary ASE usually
cannot be used as a valid DR site if it's not up to date if/when the primary ASE becomes unavailable).
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So, can disk mirroring be used in lieu of the ASE's normal backup/restore capabilities?
From the perspective of performing a 'dump database' ... perhaps ... if you're willing to periodically suspend primary
ASE activity. The secondary ASE (ie, split mirror) could then be set aside as a 'backup' of the primary ASE.
If you need up-to-date recovery capabilities like what's provided by 'dump transaction' ... perhaps ... if the secondary
ASE is always down, the mirror halves are merged, and you're using synchronous mirroring between the two halves.
If/When the primary ASE goes down you could then split the mirror and bring up the secondary ASE ... assuming the
secondary ASE's disk mirror wasn't corrupted (very real possibility if the primary ASE's disk(s) was corrupted when the
primary ASE went down).
Assuming you use disk mirroring (ie, the split copy) as a 'backup', obviously (?) you couldn't use this method to
maintain a history of database dumps.
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Personally, I wouldn't rely on disk mirroring as a permanent backup solution.
As a temporary solution in the case of needing a 'fast' rollback/downgrade option for a failed dataserver/database
upgrade? Perhaps.
Bret Halford
In general, Sybase just certifies ASE against operating system
versions. Sybase does support the technique of backing up ASE
databases by suspending write activity in a database (by use of
the QUIESCE DATABASE command, or by shutting down the server) and
copying the devices underlying the database. It doesn't matter
to ASE what method you use to copy the devices, as long as the copy
is good.
Although highly slanted towards EMC, the writeup at
http://www.sybase.com/content/1020459/deployingfinal12_12.pdf
covers the process - you would just need to substitute in
the specifics of how you would be copying the devices.
-bret