Advanced Format drives + RAID5 + LVM + EXT4 = migraine

[Jake Peavy <djstunks@xxxxxxxxx>]

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 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.

[root@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
[root@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
[root@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

 

-- 
users mailing list
users@xxxxxxxxxxxxxxxxxxxxxxx
To unsubscribe or change subscription options:
https://admin.fedoraproject.org/mailman/listinfo/users
Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines