> -----Original Message-----
> From: veritas-bu-bounces at mailman.eng.auburn.edu
> [mailto:veritas-bu-bounces at mailman.eng.auburn.edu] On Behalf
> Of Martin, Jonathan (Contractor)
>
> Can you tell me exactly what an "image" is? When I write backups
> directly to tape now, I'm pretty sure we create LOTS of
> images on tape,
> through multistreaming, and checkpoint restart. Are "images" some how
> different from fragments. I think my terminology is a little screwed
> up, but what I think you mean is, you can't destage backups from the
> DSSU until the backup is 100% finished writing? So when I get to the
> HWM its only going to purge the backups on the DSSU that are complete,
> correct?
An image is the complete product of a backup job....it can be one or
multiple fragments.
> I'm trying to get about 15TB of storage which should cover a full
> weekend's backups, but I'm a bit concerned I'll only be getting half
> that. Stupid budget. I have to say while it should work in
> theory, I'm
> a little worried about making it work after reading your post.
You should be.
> How long are we talking? I'm either going LTO3 or DLT-S4 both easily
> capable of writing 90mb/sec which is about 5GB a minute. I should be
> able to write a terabyte in 3 hours (give or take.) If a DSSU is 1TB
> (assuming I have multiple DSSUs) is 3 hours enough to "wait" for that
> DSSU to finish dumping data?
All this assumes you aren't bottlenecking at any point in your
infrastructure.
1 tape per HBA? How many HBAs on your PCI bus?
How many HBAs and drives connected to your FC switch? Backplane
bandwidth of your switch?
> Can I continue to write to a DSSU while its dumping data to tape? I'm
> making sure this is possible from a performance standpoint, but I'm
> wondering how Netbackup reacts?
Never tried it....can't imagine it would be a good thing.....big
performance hit, in addition to the items I mentioned above.
I only have my DSSU destaging window open during periods when no backups
are running.
Also, you have to schedule your destaging...how often are you gonna
destage? There will be a latency built in there......the DSSUs don't
automatically start dumping to tape when it starts filling up......the
destaging jobs run on a schedule, as any other client backup.
>
> Are the tapes eventually written considered duplicates? That is, is a
> backup goes to DSSU then to tape, is the primary copy now the
> tape? Or
> that considered a duplicate and the original gets "expired" from the
> DSSU?
The tape copy is considered "copy 2", while the DSSU copy is "copy 1".
Even after it's destaged to tape, the DSSU remains primary, as long as
the image remains on disk....when the image is expunged from the disk,
"copy 2" (the tape) automatically becomes the primary....it's still copy
2, but netbackup identifies it as the "primary" so it will be the first
contact for restores.
Paul
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