Janek Kozicki schrieb:
hold on. This might be related to raid chunk positioning with respect
to LVM chunk positioning. If they interfere there indeed may be some
performance drop. Best to make sure that those chunks are aligned together.
Interesting. I'm seeing a 20% performance drop too, with default RAID
and LVM chunk sizes of 64K and 4M, respectively. Since 64K divides 4M
evenly, I'd think there shouldn't be such a big performance penalty.
It's not like I care that much, I only have 100 Mbps ethernet anyway.
I'm just wondering...
$ hdparm -t /dev/md0
/dev/md0:
Timing buffered disk reads: 148 MB in 3.01 seconds = 49.13 MB/sec
$ hdparm -t /dev/dm-0
/dev/dm-0:
Timing buffered disk reads: 116 MB in 3.04 seconds = 38.20 MB/sec
dm doesn't do anything fancy to justify the drop (encryption etc). In
fact, it doesn't do much at all yet - I intend to use it to join
multiple arrays in the future when I have drives of different sizes, but
right now, I only have 500GB drives. So it's just one PV in one VG in
one LV.
Here's some more info:
$ mdadm -D /dev/md0
/dev/md0:
Version : 00.90.03
Creation Time : Sat Nov 24 12:15:48 2007
Raid Level : raid5
Array Size : 976767872 (931.52 GiB 1000.21 GB)
Used Dev Size : 488383936 (465.76 GiB 500.11 GB)
Raid Devices : 3
Total Devices : 3
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Tue Feb 19 01:18:26 2008
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
UUID : d41fe8a6:84b0f97a:8ac8b21a:819833c6 (local to host
quassel)
Events : 0.330016
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1
2 8 81 2 active sync /dev/sdf1
$ pvdisplay
--- Physical volume ---
PV Name /dev/md0
VG Name raid
PV Size 931,52 GB / not usable 2,69 MB
Allocatable yes (but full)
PE Size (KByte) 4096
Total PE 238468
Free PE 0
Allocated PE 238468
PV UUID KadH5k-9Cie-dn5Y-eNow-g4It-lfuI-XqNIet
$ vgdisplay
--- Volume group ---
VG Name raid
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 4
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 1
Act PV 1
VG Size 931,52 GB
PE Size 4,00 MB
Total PE 238468
Alloc PE / Size 238468 / 931,52 GB
Free PE / Size 0 / 0
VG UUID AW9yaV-B3EM-pRLN-RTIK-LEOd-bfae-3Vx3BC
$ lvdisplay
--- Logical volume ---
LV Name /dev/raid/raid
VG Name raid
LV UUID eWIRs8-SFyv-lnix-Gk72-Lu9E-Ku7j-iMIv92
LV Write Access read/write
LV Status available
# open 1
LV Size 931,52 GB
Current LE 238468
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:0
--
Oliver
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