I have an array with 4 disks in RAID 10 configuration :
root@backup:~# mdadm --detail /dev/md127
/dev/md127:
Version : 1.2
Creation Time : Mon Feb 23 16:01:29 2015
Raid Level : raid10
Array Size : 7813774336 (7451.80 GiB 8001.30 GB)
Used Dev Size : 3906887168 (3725.90 GiB 4000.65 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Tue Feb 24 11:45:12 2015
State : active, resyncing
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : near=2
Chunk Size : 512K
Resync Status : 10% complete
Name : backup:0 (local to host backup)
UUID : 8ca2df76:fc340771:56daf467:973de253
Events : 34
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
2 8 48 2 active sync /dev/sdd
3 8 64 3 active sync /dev/sde
the volume is put in a lvm device, and mapped to a logical volume using lvm
root@backup:~# pvs
PV VG Fmt Attr PSize PFree
/dev/md127 storage lvm2 a-- 7.28t 0
root@backup:~# lvs
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
root backup-vg -wi-ao--- 95.14g
swap_1 backup-vg -wi-ao--- 15.87g
diskbackup storage -wi-a---- 7.28t
The array is currently doing its initial sync :
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md127 : active raid10 sde[3] sdc[1] sdd[2] sdb[0]
7813774336 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
[==>..................] resync = 11.4% (891766016/7813774336) finish=335.0min speed=344363K/sec
now as soon as I mount the logical volume, the speed drops drastically from around 350mb/sec to 60mb/sec after a few minutes :
root@backup:~# df
/dev/mapper/storage-diskbackup 7752074548 51360 7361318244 1% /diskbackup
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md127 : active raid10 sde[3] sdc[1] sdd[2] sdb[0]
7813774336 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
[==>..................] resync = 11.8% (929634496/7813774336) finish=1780.1min speed=64454K/sec
if I reboot the server with the filesystem in fstab to automount it, the sync process runs even slower at 1500 KB/Sec
Any clues?