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[linux-lvm] LVM2 seems to chop performance by 33%



Hi

I didn't think lvm2 had such a big performance hit?

65Mb/s on the raid5 device
44Mb/s on the lv

Is this expected?

Kernel 2.6.6

representative dd's:

cu:/huge/editing/tmp# time dd if=/dev/video_vg/video_lv of=/dev/null bs=1024k count=4k
4096+0 records in
4096+0 records out
4294967296 bytes transferred in 97.363340 seconds (44112777 bytes/sec)


real    1m37.437s
user    0m0.027s
sys     0m27.126s

yet:
cu:/huge/editing/tmp# time dd if=/dev/md0 of=/dev/null bs=1024k count=4k
4096+0 records in
4096+0 records out
4294967296 bytes transferred in 65.715222 seconds (65357267 bytes/sec)

real    1m5.770s
user    0m0.026s
sys     0m27.524s


cu:/huge/editing/tmp# lvdisplay /dev/video_vg/video_lv --- Logical volume --- LV Name /dev/video_vg/video_lv VG Name video_vg LV UUID hyCwfR-d7ZG-lptP-XJFK-vMUb-JWE8-LgQSbb LV Write Access read/write LV Status available # open 2 LV Size 935.00 GB Current LE 14960 Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:0

Changing Read ahead makes no difference (actually it slows it down a touch with values of 10 + 100)

cu:/huge/editing/tmp# vgdisplay /dev/video_vg
 --- Volume group ---
 VG Name               video_vg
 System ID
 Format                lvm2
 Metadata Areas        1
 Metadata Sequence No  6
 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               935.00 GB
 PE Size               64.00 MB
 Total PE              14960
 Alloc PE / Size       14960 / 935.00 GB
 Free  PE / Size       0 / 0
 VG UUID               kFVbcB-UgLa-XQjy-mF7R-BT2D-sUaA-uGUmeK

cu:/huge/editing/tmp# pvdisplay /dev/md0
 --- Physical volume ---
 PV Name               /dev/md0
 VG Name               video_vg
 PV Size               935.00 GB / not usable 0
 Allocatable           yes (but full)
 PE Size (KByte)       65536
 Total PE              14960
 Free PE               0
 Allocated PE          14960
 PV UUID               pEWAKP-tbaH-DSXP-W2jF-Pg6H-2z35-k1adQj



David


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