Re: new database server build - sanity check

From: De DBA <>
Date: Wed, 30 Jan 2013 08:44:23 +1000
Message-ID: <>

Hi Joel,

ZFS snapshots are just like Windows shadow copies or VMWare disk snapshots a preservation of the momentary state of the disk. They require the same precautions for Oracle databases as straight filesystem copies AFAIK. That is, set the database in backup mode before snapping and return it to normal after. The snapshot gradually requires more disk space as altered blocks are preserved and thus duplicated. If you have a very active database, you'll need a LOT of free space! No additional software is required for this process.

They are useless as a DR solution, or even as a backup, unless you copy (zfs send) them to another location (tape). The snapshot is part of the file system, so if the disk fails, you loose the snapshot with it. I guess it would be better to compare the zfs snapshot with database flashback to a guaranteed restore point.


On 30/01/13 04:02, Chris King wrote:
> Sounds like ZFS snapshots could be a good backup or even a DR strategy? Is extra/specific software required to take/use snapshots for live/open Oracle databases? Or does the database have to be closed to do this?
> **
> The snapshot capabilities can be a nice feature. You can snap a live database and restore it
> back
> within moments -- eliminating the time needed for an RMAN restore.
> Having said that, I would look into testing some things
> -- perhaps Google "ZFS evil tuning guide" -- Note however, that there
> are also websites out there that discount much of what is in the guide,
> essentially saying to leave the defaults or most of them, hence some testing
> first. The foundation you lay will be
> the one you will be using.
> Joel Patterson
> Database Administrator
> 904 727-2546
> --

Received on Tue Jan 29 2013 - 23:44:23 CET

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