On Wed, 2006-08-16 at 14:37 +0100, Davina Treiber wrote:
> Nico De Ranter wrote:
> 
> >That's what I meant. If Networker somehow decided the tape isn't worth
> >writing it should flag it as bad (and of course move on to the next
> >tape) so the next time it won't be reused either.
> >  
> >
> The problem with doing that is that NetWorker doesn't know why the error 
> occurred. It could be a bad tape, or a drive problem, or a SAN or SCSI 
> problem. If it refused to re-use a tape after every SCSI error no matter 
> what the cause you would accumulate a LOT of bad tapes.

Point taken.

> >Unfortunately I cannot find anything in the logs that would indicate why
> >it's giving up on the tape. However the following message keeps popping
> >up every once in a while (but NOT for all tapes that have only been
> >partialy used):
> >
> >daemon.001:08/10/06 13:13:06 nsrd: media notice: Volume "4640" on device
> >"/dev/rmt/5hbn": Block size is 32768 bytes not 65536 bytes. Verify the
> >device configuration. Tape positioning by record is disabled.
> >
> >Shouldn't the block size depend on the device, not the tape? In that
> >case why doesn't he complain about this for *every* tape?
> >  
> >
> This almost certainly doesn't mean that your block sizes are wrongly 
> configured. It means that NetWorker has tried to read a block and has 
> read something that it does not understand.

Ah, makes sense, as I've been looking around and can't find any reason
why the block size would be incorrect. unfortunately it doesn't help in
finding what the real problem is.

> >Can I safely change the block size settings without invalidating all my
> >existing tapes (the manual seems to suggest that's not possible)
> >  
> >
> No - you don't need to change your block sizes, they are probably not wrong.

> Just as an aside, you mentioned in your original post that you get 105GB 
> on an LTO-1 tape and this post shows you are using the hbn device. You 
> could get much better performance both in terms of speed and capacity by 
> using the cbn (compressed) device. You may typically get twice as much 
> or even more on each tape depending on the data you are backing up.

The bulk of the data we backup is already gzip compressed so we figured
adding compression on the tape wouldn't help and could only slow things
down.  We've had some bad experiences with using compression on tape
devices. Granted that was about 10 years ago.

If I would switch to using the cbn device now, would I still be able to
read my existing uncompressed tapes using that device?

Thanks

Nico

-- 
Nico De Ranter
Senior System Administrator
Sony Service Center (NSCE)
The Corporate Village, Da Vincilaan 7-D1
B-1935 Zaventem, Belgium
Telephone: +32 (0)2 700 86 41 Fax: +32 (0)2 700 86 22

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