George, Brett,
On 23/12/2009, at 15:18 , George Sinclair wrote:
> bbartick wrote:
>> We recently rolled out a VTL and I'm in the process of scripting the cloning
>> process. From the testing I've done, it seems as though nsrclone does not
>> clone the SSIDs in the order you pass to the command.
>> I'd love to clone the oldest savesets first so that I can roll them off the
>> VTL first.
>> I was thinking I could do something similar to:
>> mminfo -ot -q "pool=VTL1,copies=1,!incomplete,savetime<21 days ago" -r ssid
>> --> output to a file $FILE
>
> I've run into this many times. I think it wants to best preserve the
> interleaving as it is on the original/source tapes. As a result, if, for
> example, five save sets are wrapped (multiplexed) together on the original
> volumes then that's how it wants to leave those when it writes those to the
> clones.
Yes, since NetWorker keeps multiplexing, it needs to re-order any list of
received savesets in the best order to preserve interleaving and prevent
seeks/rewinds on each piece of media it encounters.
I believe, though I've not done sufficient testing, that when cloning from
ADV_FILE -> tape you'll get the clone happening in the order requested, since
each saveset has a file# on the disk backup unit of 0, meaning that in order of
access they're all equal.
> However, if you instead run separate nsrclone commands for each ssid then
> that will force it to clone each one separately. It has to. And I don't see
> how that would eat up more space on physical clone tapes than it would if it
> preserved the interleaving, but it will certainly take longer and is more
> inefficient. That may not be a viable option for you, though, and I'm sure
> you already considered that.
To be more accurate, I'd describe this as being hideously longer/inefficient.
The reason for this is that at the end of each write operation, NetWorker will
(for want of a better term) pause for a moment before writing the 2x EOF
markers at the end of the media.
Thus, if you're cloning one saveset at a time, you're doing the following:
read+write
(pause)
write double-EOF
for next saveset:
backtrack one EOF
read+write
(pause)
write double-EOF
In actual fact it's about as "sub-optimal" as you can get. Furthermore, if you
don't time it properly and you have multiple devices, you'll find that the
first volume/device written to is still busy when you attempt to clone the
second saveset, resulting in NetWorker wanting to conduct the clone operation
on another drive/volume, meaning that savesets will then be spread out in a
worst-case layout.
Cheers,
Preston.
--
Preston de Guise
http://www.enterprisesystemsbackup.com "Enterprise Systems Backup and
Recovery: A corporate insurance policy"
http://nsrd.info/blog NetWorker Blog
http://iamtheanticloud.wordpress.com Confused about Cloud? Get a
fresh opinion here
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