Paul,
On Wed, Dec 13, 2006 at 10:37:16PM +0100, Paul Bijnens wrote:
> Brian Cuttler schreef:
> >An interesting but confusing (for me) read, but the wiki page
> >was very helpful.
> >
> >http://wiki.zmanda.com/index.php/Splitting_dumps_across_tapes
> >
> >We are will likely be implementing this shortly, I have a number
> >of jukeboxes with large DLE or many small DLE where I'm only
> >partially filling multiple tapes, I have a related question.
> >
> >Is there a value in trying to match the tape_slitsize to the chunksize ?
>
> They are completely unrelated, and can be used orthogonal.
>
> "chunksize" is a holdingdisk parameter mainly to overcome filesize
> limitations on certain filesystems. One additional benefit is that
> when using many holdingdisk areas, one dump one holdingdisk can be
> spread over all these disks, even if each of them would be too small
> to hold one complete image.
Understood, had just been wondering if there was any benefit to
having them match, ie, is there any efficiency to having each
be 1 Gig for instance, does it save anything when part of the process
is to assemble chunks and the other part of the process is to take
the data streem and chunk it for output.
I would suppose that even if the chunksizes where the same the
boundries would be different. Making the point moot, but I thought
I'd ask.
> "tapesplit_size" is the size of chunk on tape. When writing such
> a chunk to tape, and the tape bumps into EOT, the next tape is loaded,
> and the complete chunk is rewritten again. Compare this to the
> alternative to restart the complete dumpimage on that tape: it
> avoids wasting too much tape (and time writing it).
Yes, we have at this time several jukebox enabled systems with many
DLE and some of the output tapes end up with perhaps 60 % utilization.
I would actually end up with a 4 tape run rather than a 5, useful not
only for elapse time but cost savings for media.
> Note also that tapesplit_size is a dumptype parameter: you may
> specify which DLE's should be split, and which not (e.g. not
> splitting the DLE's that contain the amanda software makes
> restores easier, when that disk itself was lost).
While reading the wiki (again, very nicely written) I took note of
that I realized the implications immediately. Allow chunking of
the large user drives, don't allow it for the root partition, that
sort of thing. Prior to reading the wiki I hadn't realized that and
had (incorrectly) assumed it was a (binary) taper switch.
Thank you for helping to clear this up.
Brian
> --
> Paul Bijnens, Xplanation Tel +32 16 397.511
> Technologielaan 21 bus 2, B-3001 Leuven, BELGIUM Fax +32 16 397.512
> http://www.xplanation.com/ email: Paul.Bijnens AT xplanation DOT com
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---
Brian R Cuttler brian.cuttler AT wadsworth DOT org
Computer Systems Support (v) 518 486-1697
Wadsworth Center (f) 518 473-6384
NYS Department of Health Help Desk 518 473-0773
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