Hey all,
I'm going a little off my rocker here trying to understand how to best
configure a 3-drive RAID5 array using the new Western Digital 4k sector
drives.
I've got 3xWD15EARS (1.5T 4k sector advanced format drives).
If I was using the drive as-is, my understanding is I should create a
partition starting at sector 64. This would solve all my problems.
But I want to put them into a RAID5 array, so currently I didn't partition
at all and just passed mdadm the whole drive. Not sure if this is the best
approach. I used 512kB as chunk size.
Then I want to create LVM on the array. I didn't pass any special parms to
{pv,vg,lv}create (should I?)
Lastly, I want to create an EXT4 filesystem on the array. I used the stride
calculator at
http://busybox.net/~aldot/mkfs_stride.html<http://busybox.net/%7Ealdot/mkfs_stride.html>
with
raid level = 5, devices = 3, chunk size = 512 and filesystem blocks = 4 (?)
which suggested I use mkfs.ext4 -b 4096 -E stride=128,stripe-width=256
(which I did).
After doing all this, I get writes to my filesystem of only 38MB/s. Reads
of 119MB/s.
[r...@morbo opt]# hdparm -Tt /dev/mapper/array_vg-lv_opt
/dev/mapper/array_vg-lv_opt:
Timing cached reads: 1574 MB in 2.00 seconds = 786.85 MB/sec
Timing buffered disk reads: 332 MB in 3.00 seconds = 110.57 MB/sec
[r...@morbo opt]# time (dd if=/dev/zero of=zerofile bs=1M count=8192; sync)
8192+0 records in
8192+0 records out
8589934592 bytes (8.6 GB) copied, 226.646 s, 37.9 MB/s
real 3m51.062s
user 0m0.072s
sys 0m39.794s
[r...@morbo opt]# dd if=zerofile of=/dev/null bs=1M
8192+0 records in
8192+0 records out
8589934592 bytes (8.6 GB) copied, 72.4094 s, 119 MB/s
I have a feeling my array should perform much better than this and it's
probably because I haven't taken the 4k sector size into account and I'm
bleeding performance.
Can anyone comment? If I need to take the 4k sector size into account,
where should I do so? With partitions? In pvcreate? Some other place? Or
multiple places?
TIA,
--
-jp
If you ever go temporarily insane, don't shoot somebody, like a lot of
people do. Instead, try to get some weeding done, because you'd really be
surprised.
deepthoughtsbyjackhandey.com
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