On Tue, 18 Dec 2007, Thiemo Nagel wrote:
Performance of the raw device is fair:
# dd if=/dev/md2 of=/dev/zero bs=128k count=64k
8589934592 bytes (8.6 GB) copied, 15.6071 seconds, 550 MB/s
Somewhat less through ext3 (created with -E stride=64):
# dd if=largetestfile of=/dev/zero bs=128k count=64k
8589934592 bytes (8.6 GB) copied, 26.4103 seconds, 325 MB/s
Quite slow?
10 disks (raptors) raid 5 on regular sata controllers:
# dd if=/dev/md3 of=/dev/zero bs=128k count=64k
8589934592 bytes (8.6 GB) copied, 10.718 seconds, 801 MB/s
# dd if=bigfile of=/dev/zero bs=128k count=64k
3640379392 bytes (3.6 GB) copied, 6.58454 seconds, 553 MB/s
Interesting. Any ideas what could be the reason? How much do you get from a
single drive? -- The Samsung HD501LJ that I'm using gives ~84MB/s when
reading from the beginning of the disk.
With RAID 5 I'm getting slightly better results (though I really wonder why,
since naively I would expect identical read performance) but that does only
account for a small part of the difference:
16k read 64k write
chunk
size RAID 5 RAID 6 RAID 5 RAID 6
128k 492 497 268 270
256k 615 530 288 270
512k 625 607 230 174
1024k 650 620 170 75
Kind regards,
Thiemo
# dd if=/dev/sdc of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 13.8108 seconds, 77.7 MB/s
With more than 2x the drives I'd think you'd have faster speed, perhaps
the contoller is the problem?
I am using ICH8R (but the raid within linux) and 2 port SATA cards, each
has their own dedicated bandwidth via PCI-e bus.
I have also tried (on 3ware controllers exporting as JBOD etc, sw RAID5)
with 10 disks, I saw similar performance with read but not write.
Justin.
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