I backup zfs data to ibm lto4 tape drive using zfs send then dd to tape with transfer rate about 30MB/s but when I try to restore using dd from tape drive it transfer rate is about 7MB/s. Is this normal transfer rate of lto4 tape drive on solaris 10?
my command to restore from tape
dd if=/dev/rmt/0cbn of=/dev/null bs=131072
What am I doing wrong? from lto4 datasheet say it transfer rate about 30MB/s - 120 MB/s
Edited by: user13259844 on Apr 12, 2013 3:45 AM
It's not normal transfer rate for LTO4.
Please show result
iostat -xnz 2 3
when dd work.
Please show mt -f /dev/rmt/ocbn when cartridge is loaded.
What type of cartridge you are use ?
How tape drive connected to you server ? ( FC / SAS ? )
iostat show that bottleneck is tape ( busy 97% ).
It strange small size of block :
462.6 0.0 8330.9 0.0 0.0 1.0 0.0 2.1 1 97 rmt/0
BS=8330.9 / 462.6 ~ 18 kB
Try make some test on new tape:
dd if=/dev/zero of=/dev/rmt/0n bs=128k count=8192
dd if=/dev/rmt/0n of=/dev/null bs=128k
and see iostat output on other terminal.
after change bs=128k to ibs=128k obs=128k for backup to tape then restore it get transfer rate about 43 MB/sec.
dont know why bs=128k not equal ibs and obs but it is enough time for my restore window now.