Re: tar's default block size & shoe-shinning

Does anybody knows about the --with-maxtapeblocksize used by RedHat ES 3.3?

Cyrille

Joshua Baker-LePain <jlb17 AT duke DOT edu>
Envoyé par : owner-amanda-users AT amanda DOT org

19/06/2006 11:02

A	Cyrille Bollu <Cyrille.Bollu AT fedasil DOT be>
cc	amanda-users AT amanda DOT org
Objet	Re: tar's default block size & shoe-shinning

On Mon, 19 Jun 2006 at 10:05am, Cyrille Bollu wrote > Could someone tell me if there are any possibilities to change the block > size tar is using when backuping with amanda? > > I'm asking this because we have recently bought an IBM ULTRIUM-TD3 LTO3 > drive here and Amanda reports an average write rate of only 17MB/s (when > the maximum speed should be 40 MB/s uncompressed). Which most probably > means that the drive is shoe-shinning... Actually, native speed of LTO3 is 80MB/s, but it can throttle back to 1/2 that without shoeshining. So 40MB/s is the slowest you want to see. > I think, tar's default block size of 10k is the most limiting factor since > the constructor recommends a block size of 64kb and tests with "dd" > reported a transfer speed of 33MB/s with bs=64k and only reports a 25MB/s > with bs=10k. Amanda doesn't 'tar' directly to tape, so it's not tar's blocksize you need to change. Amanda does its writing to tape with a default blocksize of 32KiB. To change that, you'll need to recompile amanda and specify the --with-maxtapeblocksize option to configure. With my LTO3 drive, I compile amanda with --with-maxtapeblocksize=2048. After recompiling amanda, you can change the blocksize in the tapetype. Mine says "blocksize 2048", for a 2MiB blocksize. My backups generally tape at >60MiB/s. > bs time (sec) calculated speed (MB/s) > =================================== > 64k 95 33,7 > 32k 100 32 > 10k 130 24,6 > 4k 173 18,5 > 1k 409 7,8 > > (results from the command "time dd if=/dev/sda2 of=/dev/nst0 bs=<var1> > count=<var2>". Where <var2> is calculated so that <var1>*<var2>=3200MB) *All* of those speeds are too slow, so you probably want to look at bigger blocksizes. Also note that there's no way a single disk can both accept backups from over the network *and* keep an LTO3 drive streaming. I drive my LTO3 drive with a 4-disk RAID0, and I'm looking at going bigger so I can use the 2nd drive in my library simultaneously. -- Joshua Baker-LePain Department of Biomedical Engineering Duke University