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Re: Oracle backups using Snapshot Technology

From: Mark Brinsmead <>
Date: Wed, 8 Nov 2006 21:51:17 -0700
Message-ID: <>

I remember a time (not so long ago) when performing backup backups with "snapshot" technology was cutting edge, and SAN-based "server-free" backups were considered the holy-grail of backup and recovery. Of course, that was back in the days when the best (and most expensive) tape drive technologies did maybe 20MB/s and cost in the neighbourhood of $50,000 each.

I had a client once who was fully prepared to spend $2Million for hardware to backup a 600GB database -- $1Million for tape drives, and $1Million for a massive robot (hypothetically) capable of doing 15,000 tape changes per night.

In cases where you have really extreme backup requirements (e.g., terabyte+ database running flat-out 24x7 on the biggest hardware you can find) snapshot technologies can be a godsend. They might be the only option available.

But they are not cheap. On most storage platforms I have seen, "snapshot" backups are an extr-cost option, often in the range of $50,000 to $100,000. With modern tape drives managing sustained throughput in the neighbourhood of 500GB/hr -- for the "enormous" cost of about $7000 per unit, you can purchase a lot of backup throughput for the cost of the "snapshot" option for one mid-range disk array.

Also beware of unrealistic expectations, and impossible promises. I have actually worked at sites where the storage managers actually believed that a "snapshot" terabyte volume could complete "nearly instantaneously". Heck, I knew one manager who believed he could do "snapshots" of 30TB of data in only a few minutes -- between two baby EMC disk arrays. I show him numbers that proved that running half of the interfaces in each array flat-out, these "snapshots" would take something on the order of 30 hours to complete, but he knew I was wrong -- after all, the sales rep told him they were "instant"...

In general, "snapshots" take only moments to initiate, and you can start reading from the almost instantly. (This is the amount of time your database needs to be in "backup" mode.) But depending on the data volumes, they can take hours, or even days to complete. Until the snapshot has completed -- or been read in its entirity and copied to tape -- you don't actually have a backup. A disk failure in the "primary" storage during this time will destroy the "snapshot", too!

Personally, I think the "snapshot" thing is really cool -- and it was even cooler back in about 1993. But I am aware of relatively few situations where this is actually needed.

To be honest, I think it is tough today to compete with the performance and cost-effectiveness of locally-attached tape drives...

Can you do "snapshot"

On 11/8/06, DIANNA GIBBS <> wrote:
> We're looking at implementing a new enterprise backup solution.
> Is anyone using "snapshot technology" to backup your oracle databases?
> If so, could I get more info - O/S, database version, database size,
> timings for putting tablespaces in backup mode (database mode if 10g),
> SGA size, good things, lessons learned, comments or thoughts?
> Have you tested the backup, recovered or refreshed an environment using
> this technology - any issues?
> What about snapshot vs RMAN - any comments?
> Thanks in advance.
> Dianna Gibbs
> Children's Medical Center - Dallas
> --

-- Mark Brinsmead
   Senior DBA,
   The Pythian Group

Received on Wed Nov 08 2006 - 22:51:17 CST

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