Re: Best Backup Blocksize for 110SDLT Tape?

From: Paul Sture (nospam_at_sture.homeip.net)
Date: 03/05/04 

Date: Fri, 05 Mar 2004 10:28:22 +0100

John Santos wrote:
>
> On 4 Mar 2004, Daryl Jones wrote:
>
> > Dear John Santos:
> >
> > The issue is not that it may pertain to 9 track tapes only. The issue
> > raised was that is or was a problem with tape backup and restores
> > using block size greater than 32256 and nobody had a solution or
> > understanding of the problem. That by itself is worry some.
>
> No one else has ever experienced or heard of any such problem, AFAIK.
>
> I certainly haven't, and I've been doing VMS backups (and restores)
> since VMS backup was released (V3.0?)
>

Same here. ISTR a recommendation with the VaxStation 2000 and TK50/TK70
drives
that you didn't use block sizes greater than 16K, due to the I/O
architecture.

I never experienced the "joys" of Exabyte tapes, but did hear some
horror stories.

> The *only* problem with blocksize > 32256 is the documented restriction
> that the resulting ANSI tape files can't be copied to disk. Restore
> from tape has *always* (AFAICR) worked fine.
>

I've just thought of another use for this, implicit the ability to copy
to disk.

You can also copy across networks, which can be very useful for DR
purposes. In that case you should also check that your network setup can
handle your chosen blocksize
(just something niggling at the back of my mind there, so it needs
testing).

So back to the original question. If SDLTs give a sufficient performance
improvement
by using 65024 blocksize, then use that, but be aware that you will not
be able to
copy the savesets to disk or across the network. If you can think of a
situation
where that would be useful, accept it as a compromise.

Only you can weigh up the proc and cons for your site, and there's no
substitute for rigorous testing on your own hardware mix. 

-- 
Paul Sture

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