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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?

1 Answer 1

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I found the cause. EXT4 is populating inode list since it is a freshly created filesystem which causes the rebuild speed to drop.

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  • seems to be so - and there are some tips there to speed it up which might be relevant too.
    – Zanna
    Aug 24, 2017 at 15:15

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