On Wednesday 04 January 2006 05:13, Hommersom, Gerrit (G) wrote:
>I've followed with great interest the discussion on this topic as it
>pertains to my backup system
>
>The problems with premature end-of-tape failures persist with big
> DLE's. (order 30-35 GB). The problem gets more severe from 1 failure
> per cycle to daily failures currently. No dumps are left on the
> holding disk.
>
>Closer inspection of the Exabyte FAQ learned that this may occur if
> the datarate to the drive is too low. The drive waits for input
> while writing 'gap tracks' that uses physical space.
>
>I re-examined the amanda logs and saw that for large DLE's the
> datarate for the dumper and taper are the same and in the order of
> 3300 KB/s. VXA2 units write at 6000 KB/s

This, if the holding disk is actually being used, is immaterial as long 
as the hdparm -tT on the holding disk exceeds the 6Mb/sec that the vxa 
needs. Even with DMA turned off, it should be able to do that..

If the holding disk is in use, the dle will be written to it in its 
entirety before the transfer to the tape occurs, at which point it 
will be copied at the speed the interface is capable of.

>The main raid-5 taperack is an external SCSI2 unit. The tape is
> external SCSI2 too. The holding disk is 39 GB on an internal SCSI2
> disk.
>
Compare the calculated size of the reserved amount of the holding disk 
(default 100%) and the size of the dle.  I'd assume that since no 
files are being left on the holding disk, that it is indeed not being 
used, at which point those speeds you quote above then apply.  If my 
holding disk was 39GB, then I certainly wouldn't reserve more than 15 
to 20%, or might even specify it as a -nGB format, which would let it 
use up to the nGB remaining for fulls.

See your amanda.conf for this reserved keyword and its usage.

>My questions:
>will amanda use the holding disk for DLE's from on local disk to
> another i.e. will DLE's from the external filsystem use the holding
> disk before taping.
>I accidentally defined a holdingdisk chunksize of 10 GB on a standard
> (32 bit) linux system. What would be the effect: direct write to
> tape ?? will the network bandwith parameters affect backup speed of
> local disks?? What factors may affect the datarate to the tape unit
> ??

Holding disk, use/non-use will be the single most important controlling 
factor.  Anything else is way down the list in importance.

>Thanks
>Gerrit Hommersom

-- 
Cheers Gerrit, Gene
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