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nichot20
January 19th, 2010, 12:30 AM
Some time ago I built an Amanda 2.5.x system on SuSE 10.3 (using the repo version) with an IBM Ultra 160 scsi LTO3 and was getting amtapetype figures of around 65000 kp/s.

I recently built a second system on Suse 11.1, again using the repo version 2.5.2.1 on an IBM x3550 with a Quantum SAS LTO4 connected via an LSI SAS3801E. This only gave me ~45000 kp/s.

Rebuilding the above to Suse 11.2 and the supplied 2.6.1.1-3.4 dropped this figure even more to ~37000 kp/s, a figure confirmed by a third build on a different cpu but the same other components.

I get over 200MB/s writing through the HBA to a SAS raid, and an LTO4 should be good for 120MB/s and is audibly spending a lot of time waiting, so why the pants performance?:confused:

Incidentally, what is the relation between the amtapetype "kp/s" and the more usual measure of throughput in MB/s? I presume it stands for kilo packets/sec but I am not sure of the packet size, its clearly not the block size.

nichot20
January 21st, 2010, 01:30 AM
OK so I think I may be getting to the root of this.
I have run some tests using "dd if=/RAID/randombytefile of=/dev/nst0 bs=NNNk" with varying values of NNN (the blocksize)
NNN Throughput
32k 44MB/s *Not too disimilar to amtapetype figure.
128k 90MB/s
256k 88MB/s
512k 86MB/s

From this it would seem that Amanda's default 32K blocksize is severely limiting the performance on more modern faster tape units.

nichot20
January 25th, 2010, 03:38 AM
OK, So I think I have answered my own query.
MY original build was on 2.5.2p1-1, and my build had a fixed blocksize such that changing that parameter made no difference to amtapetype. However I now find that on my build of 2.6.1.1p1 this is no longer true and after trying various figures have come up with the following amtapetype results:-

#Z400 based system
define tapetype quantum-lto4-256 {
comment "Created by amtapetype; compression enabled"
length 815598080 kbytes
filemark 5688 kbytes
speed 75434 kps
blocksize 256 kbytes
}
#IBM x3550 system
define tapetype quantum-lto4-256 {
comment "Created by amtapetype; compression enabled"
length 815319040 kbytes
filemark 4543 kbytes
speed 77597 kps
blocksize 256 kbytes
}
Running an actual dump on the Z400 system showed TAPER STATS as going up from ~36MB/s to ~89MB/s
Job Done :)