On Thu, 24 Apr 2003, Russell Adams wrote:

> The host runs OpenVMS, and the only reason this is relevant is because
> I'm constantly wishing I could run AMANDA on this platform. VMS's
> BACKUP utility doesn't support compression, or anything else for that
> matter. Our backups are done by custom scripts. If I ran Tru64 or
> Linux on these, I'd be using AMANDA.
>
> Because of the benchmarked performance with these tape drives, I've
> often wanted to use client side compression due to the amount of
> horsepower available. I cannot due to software constraints.

Oh wow.  VMS backup.  I haven't touched that in nearly a decade.  I
wonder if anyone has tried to mate it to amanda.  I'm half thinking
it might be possible, but my VMS memory is getting very rusty and
whole chunks have no doubt been overwritten.  If you can get the amanda
client to build, you might be able to do the gnutar wrapper trick to
have amanda call a wrapper script in lieu of gnutar, and the wrapper
script then calls backup.  If you can redirect the output of backup
into something resembling a pipe then it should be possible.  If you're
willing to put some development time into it.


> Quite frustrating when the disk to disk copy takes 4 hours, then it
> takes 14 hours to back it all up to tape.
>
> In uncompressed mode I get 4-5MB/s, in compressed its 800KB/s. Sad
> really.

This still bothers me.  As long as you're able to feed data to the tape
fast enough to keep it streaming, it should do 4-5 MB/s or faster.  With
data that compresses 2:1 it should do ~ 10 Mb/s.  Oh...  Ah-hah!  Now I
get it.  You're keeping up with it at 5 MB/s, but when you put it in
compressing mode it can eat data that much faster, so now you've got to
feed it faster to keep it streaming.  You're not able to feed it 10 MB/s,
so it's having to do the stop/rewind/start thing over and over.

If you have enough disk you can try to emulate amanda's holding disk
feature.  Do your backups to an empty holding disk and then once a
backup image is complete, copy it to tape.  Copy should be able to keep
it streaming.   OR...  upgrade the DLT7000s to DLT8000s.  They can do
variable speed writing, at the cost of less capacity per tape cartridge.

-Mitch