On Wed, 15 May 2002, John Orthoefer wrote:
> So we didn't scare you off with our diskscrubbing advice. *smile*
>
> Yep this is a classic mainframe backup technique. You make a triple
> mirror (Master + 2 mirrors) then when you want to back up your database you
>
> * stop accepting transactions
> * clear all the pending transactions
> * break one mirror off
> * enable transactions
> * mount the mirror read-only back onto your database
> * back up the ro copy of the db
> * unmount the ro copy
> * reattach and sync the mirror to the master database
>
> That way you still have your mirror with current pending transactions
> even if you are in the middle of doing a backup. And the downtime for
> the backup can be just a few seconds. This was used in the day when
> RAID systems wheren't that common. Today I would use either 2 raid
> systems, or even a raid system, and some JBOD for the backup mirror.
>
> Since EMC is still a mainframe disk company, the Syms can do this sort
> of thing. I've never used it, but with all the support that EMC
> offers, you should be able to cut a deal to get setup working with your
> rep.
BCV (and SRDF) is intended for real-time data protection, so that you will
be able to recover your data in any case. It is intended to work in real
time and if you have a once-a-day sync requirement, it is an overkill.
There are few things, which worth checking:
1. If there is a support contract for the Symm in effect, they answer all
mirror-related questions and they can set it up for you.
2. EMC Foundation Suit (if you have one) is actually a relabeled Veritas
and you can do snapshots/mirrors, etc. on fly. The only difference between
EFS and Veritas are a few "rules", which improve data throughput, like
increase of I/O size from 64 K to 128 K, because Symm likes it more.
3. Disks in your Symm are quite possibly already mirrored, this is a
standard setup. You can add a third mirror to it, or split a mirror
temporarily, for backup purposes, etc., as by John Orthoefer described
above.
4. If you are mirrored already, than you don't need to worry, Symm will
call home if one half of mirror will fail and some tech with a new drive
will come next morning.
>
> Netapp has the same functionality, it's call snap mirror I think.
> Again, you are talking about spending a bit of cash with netapp. They
> should give you engineering support to make it work.
>
Netapp can do the same, but it costs some extra.
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Dimitri (Dima) Shcherban
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