Backup Software

We are using SAN for the SQL Server 2000.
Someone mentions that since SQL Server is using cache during operation, when
we do the sanpshot of the SAN, the cache value has to be written to SAN. Is
it correct, what is the exact steps for this mechanism ?
Thanks"Robert" <Robert@.discussions.microsoft.com> wrote in message
news:u0bsYJ5iGHA.4884@.TK2MSFTNGP03.phx.gbl...
> We are using SAN for the SQL Server 2000.
> Someone mentions that since SQL Server is using cache during operation,
> when we do the sanpshot of the SAN, the cache value has to be written to
> SAN. Is it correct,
Yes, that is correct. In effect the backup software requests that the
databse flush it's dirty pages to disk and prepare for the snapshot, then to
suspend writes while the snapshot is taken.

>what is the exact steps for this mechanism ?
VSS the Windows Volume Shadow Copy Service.
How Volume Shadow Copy Service Works
http://technet2.microsoft.com/Windo...3.mspx?mfr=true
That's how it should work. If your SAN software doesn't use VSS then you
should not use it to snapshot SQL Server databases.
David|||Dear David,
Thank you for your prompt reply.
Can you elaborate more about dirty pages ? Why they have to be flushed to
the disk ?
Rob
"David Browne" <davidbaxterbrowne no potted meat@.hotmail.com> wrote in
message news:ekh0FS5iGHA.4884@.TK2MSFTNGP03.phx.gbl...
> "Robert" <Robert@.discussions.microsoft.com> wrote in message
> news:u0bsYJ5iGHA.4884@.TK2MSFTNGP03.phx.gbl...
> Yes, that is correct. In effect the backup software requests that the
> databse flush it's dirty pages to disk and prepare for the snapshot, then
> to suspend writes while the snapshot is taken.
>
> VSS the Windows Volume Shadow Copy Service.
> How Volume Shadow Copy Service Works
> http://technet2.microsoft.com/Windo...3.mspx?mfr=true
>
> That's how it should work. If your SAN software doesn't use VSS then you
> should not use it to snapshot SQL Server databases.
> David
>|||"Robert" <Robert@.discussions.microsoft.com> wrote in message
news:ei3PhW5iGHA.4512@.TK2MSFTNGP02.phx.gbl...
> Dear David,
> Thank you for your prompt reply.
> Can you elaborate more about dirty pages ? Why they have to be flushed to
> the disk ?
>
Dirty pages contain changes that a user has made to the database, but which
haven't been written to the data files yet. These changes have been
commited in the transaction logs, and they are real, complete, durable
transactions. If you don't flush these pages to disk before taking a
snapshot then you would loose data when restoring the database.
David