veritas-bu-bounces at mailman.eng.auburn.edu <> wrote:
[Actually it was Paul but Outlook-quotefix gets it wrong]

>> -----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. 

A backup job is usually one mount point.  So the C: drive on server A would
be one image.  The D: drive on server B would be the next image.  Back in
NetBackup 5.x, fragments were limited to 2GB so an image often consisted of
multiple fragments.  With NBU 6, fragments I believe are unlimited (or
limited to 512GB - and yes, we do have images that are larger than 512GB but
I haven't checked to see how many fragments they end up in).

>> 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.  

Achieving 90MB/sec is not easy at all.  Heck, I can't even currently destage
at more than about 30MB/sec most of the time and that's from a Sun V490 with
SAN-attached disks to a SAN-attached LTO-3.  Yes, I know I should be able to
do better, but you'd think we should be able to beat that out of the box.
What I'm saying is that it's not *easy* to write 90MB/sec.  You're going to
have to work at it.  Mine goes up and down continually and you'll be pausing
while you go from image to image so definitely do not expect an average of
90MB/sec.

>> 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?

Yes you can.  We regulary write to a DSSU and destage it at the same time.
We have backup jobs and destage jobs going around the clock.

> Never tried it....can't imagine it would be a good thing.....big
> performance hit, in addition to the items I mentioned above.

Reading and writing to a disk drive at the same time isn't that hard.
That's what disk drives do :-).  

   .../Ed

Ed Wilts
mailto:ewilts at ewilts.org
Mounds View, MN 55112