Re: [Veritas-bu] NBU Flashbackup Cache Parition

On Tue, 15 Jul 2008, dy018 wrote:
>
> Anyone of you has experience in flashbackup using solaris advanced client. Is the cache partition a mandatory requirement for Flashbackup? If it is, then anyone know the workaround? Thanks

On Tue, Jul 15, 2008 at 3:19 AM, Justin Piszcz <jpiszcz AT lucidpixels DOT com> wrote:

AFAIK you need a small raw partition for it.

Small is relative. The size of the cache volume is relative to the write rate. If your volume is read-only, then a volume large enough to hold the bitmap is probably enough. If you're hammering the heck out of it while the backups are active, you could end up needing a cache volume as large as the original volume.

The Snapshot Client Administrator guide is online and I suggest that dy018 read it before going too much farther - there's a *lot* of detail there.

The answer to the original question is documented in the manual:

"In all cases, a raw partition must be specified as cache for the snapshot. Any number of concurrent nbu_snap backups can use the same cache, if: the cache is large enough to hold copies of all file system blocks that were changed by user activity while the snapshots were active."

There are certainly other "workarounds", and that's to use a snapshot method that's not on the file system - if your disk controller supports snapshots (e.g. HP EVA, EMC Symmetrix, NetApp), trigger them instead. The main requirement is you have a method to support copy-on-write while the backups are going. In other words, do not write to the raw device being backed up.

.../Ed

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Ed Wilts, Mounds View, MN, USA
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