Jones, Stephen (East Kilbride) [OS-IE] wrote:

> I have a simple question: Does anyone use the disk backup option to restore
> from disk?
> 
> We recently implemented a disk backup solution with the intention of keeping
> our backups on disk for three days, and then staging backups older than
> three days to tape.
> 
> The whole point of this was not only to speed up backups, but also to speed
> up recoveries, mainly because a number of our systems have pretty tight
> Disaster Recovery Time Objectives. We were hoping that we could minimise our
> need to use tapes for recoveries, as the most recent data would be on disk.
> 
> In the course of the last week it has come to light that it is well nigh
> impossible to do a recovery from an advanced file device at the same time as
> you are writing data to, or staging from that advanced file device. We have
> had a few calls open with Legato and the feeling we are getting, rightly or
> wrongly, is that the disk backup option is not intended to facilitate
> restores from disk. It is primarily there to facilitate cloning and staging,
> and that restores should take place using tape - not disk.
> 
> Does anyone else have any experience of this? Is anyone else backing up to
> disk and subsequently restoring from disk? Can you do both operations
> simultaneously? 

adv-file devices support one write and one read simultaneously. You
cannot do two simultaneous reads. So in your situation the fact that you
are backing up to disk should not impact on your recovery, but the
staging operation will.

This limitation is documented. It is not a bug, just poor design, along
with other aspects of the adv_file concept.

I'm surprised that Legato Support have not been able to explain this
quickly and simply.

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