Hi,
This question might be better suited for the lvm mailing list, but
raid10 being rather new, I decided to ask here first. Feel free to
direct me elsewhere.
I want to use lvm on top of a raid10 array, as I need the snapshot
capability for backup purposes. The tuning and creation of the array
went fine, I am getting the read performance I am looking for. However
as soon as I create a VG using the array as the only PV, the raw read
performance drops to the ground. I suspect it has to do with some minima
l tuning of LVM parameters, but I am at a loss on what to tweak (and
Google is certainly evil to me today). Below I am including my
configuration and test results, please let me know if you spot anything
wrong, or have any suggestions.
Thank you!
Peter
========================
root@Arzamas:~# mdadm -D /dev/md1
/dev/md1:
Version : 00.90.03
Creation Time : Sat Jun 9 15:28:01 2007
Raid Level : raid10
Array Size : 317444096 (302.74 GiB 325.06 GB)
Used Dev Size : 238083072 (227.05 GiB 243.80 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 1
Persistence : Superblock is persistent
Update Time : Sat Jun 9 19:33:29 2007
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : near=1, far=3
Chunk Size : 1024K
UUID : c16dbfd8:8a139e54:6e26228f:2ab99bd0 (local to host
Arzamas)
Events : 0.4
Number Major Minor RaidDevice State
0 8 2 0 active sync /dev/sda2
1 8 18 1 active sync /dev/sdb2
2 8 34 2 active sync /dev/sdc2
3 8 50 3 active sync /dev/sdd2
root@Arzamas:~#
root@Arzamas:~# pvs -v
Scanning for physical volume names
PV VG Fmt Attr PSize PFree DevSize PV UUID
/dev/md1 raid10 lvm2 a- 302.73G 300.73G 302.74G
vS7gT1-WTeh-kXng-Iw7y-gzQc-1KSH-mQ1PQk
root@Arzamas:~#
root@Arzamas:~# vgs -v
Finding all volume groups
Finding volume group "raid10"
VG Attr Ext #PV #LV #SN VSize VFree VG UUID
raid10 wz--n- 4.00M 1 1 0 302.73G 300.73G
ZosHXa-B1Iu-bax1-zMDk-FUbp-37Ff-k01aOK
root@Arzamas:~#
root@Arzamas:~# lvs -v
Finding all logical volumes
LV VG #Seg Attr LSize Maj Min KMaj KMin Origin Snap% Move
Copy% Log LV UUID
space raid10 1 -wi-a- 2.00G -1 -1 253 0
i0p99S-tWFz-ELpl-bGXt-4CWz-Elr4-a1ao8f
root@Arzamas:~#
root@Arzamas:~# dd if=/dev/md1 of=/dev/null bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes (2.1 GB) copied, 11.4846 seconds, 183 MB/s
root@Arzamas:~#
root@Arzamas:~# dd if=/dev/md1 of=/dev/null bs=512 count=4000000
4000000+0 records in
4000000+0 records out
2048000000 bytes (2.0 GB) copied, 11.4032 seconds, 180 MB/s
root@Arzamas:~#
root@Arzamas:~# dd if=/dev/raid10/space of=/dev/null bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes (2.1 GB) copied, 25.7089 seconds, 81.6 MB/s
root@Arzamas:~#
root@Arzamas:~# dd if=/dev/raid10/space of=/dev/null bs=512 count=4000000
4000000+0 records in
4000000+0 records out
2048000000 bytes (2.0 GB) copied, 26.1776 seconds, 78.2 MB/s
root@Arzamas:~#
P.S. I know that dd is not the best benchmarking tool, but the
difference is so big, that even this non-scientific approach works.
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