Discrepancy between amrestore and dd speeds

Hello list,

I've been performance testing Amanda, trying to get the setup ready forprime-time, but I'm having an issue getting my read speeds from tape toget even to 6MB/s. My writes are about 12.7MB/s, which is what the tapedrive boasts (12-24MB/s normal and 2:1 compression, respectively). But,my reads seem to hover around 5.5MB/s. I ran some dd tests, which showthe data being pulled off at 11.7MB/s, and I'm not quite sure how totell what amrestore is doing that is causing the performance drop off.Here are the tests I ran; any help is appreciated.

backup@amandaserver# dd if=/dev/nst0 of=/home/restores/foobar bs=256Kcount=10000G

                                      10308+0 records in
                                      10307+0 records out

2701918208 bytes (2.7 GB) copied,230.539 seconds, 11.7 MB/s



backup@amandaserver# amrestore -r /dev/nst0 hostname /foo/bar

backup@amandaserver# stat /home/restores/hostname._foo_bar.20071216.0.1.RAW

File:`home/restores/hostname._foo_bar.20071216.0.1.RAW'Size: 2836922368 Blocks:5546275 IO Block: 131072 regular fileDevice: 908h/2312d Inode:13 Links: 1Access: (0640/-rw-r-----) Uid:( 34/ backup) Gid: ( 34/ backup)Access: 2007-12-1812:50:15.000000000 -0500Modify: 2007-12-1812:58:40.000000000 -0500Change: 2007-12-1812:58:40.000000000 -0500

So, ~8 minutes for a 2.7GB file = ~5.7MB/s. I saw similar performancewhen retrieving a DLE that spanned 6 chunks (~5.3MB/s) No errors oranything in my amrestore logs, just start and stop times. I'm kind ofat a loss as to what would be causing this, unless my calculations (size / time ) aren't valid? Thanks.


Best Regards,
Ryan

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Ryan SteeleSystems AdministratorThe Archer Group