mdadm: Linux software RAID
Installation
$ apt-get install mdadm
Usage
Check software RAID array status
Use the following command:
$ cat /proc/mdstat
or
$ mdadm -D /dev/mdX
Output in case of non-existant RAID device:
$ mdadm -D /dev/md0
Personalities :
unused devices: <none>
Output for RAID6 device:
$ mdadm -D /dev/md0
Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
md0 : active raid6 sdc[2] sda[0] sdd[3] sdb[1] sde[4]
35156259840 blocks super 1.2 level 6, 512k chunk, algorithm 2 [5/5] [UUUUU]
unused devices: <none>
A progress bar is displayed under partitions when a RAID resync process is currently running:
$ mdadm -D /dev/md0
Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
md0 : active raid6 sde[4] sdb[1] sdd[3] sda[0] sdc[2]
35156259840 blocks super 1.2 level 6, 512k chunk, algorithm 2 [5/5] [UUUUU]
[=======>.............] resync = 35.0% (4101838624/11718753280) finish=1179.1min speed=107662K/sec
unused devices: <none>
Speed up software RAID resync
Increase speed limits
Check current speed:
$ sysctl dev.raid.speed_limit_min
$ sysctl dev.raid.speed_limit_max
Increase target rebuild speed:
$ echo 50000 > /proc/sys/dev/raid/speed_limit_min
$ echo 200000 > /proc/sys/dev/raid/speed_limit_max
or
$ sysctl -w dev.raid.speed_limit_min=50000
$ sysctl -w dev.raid.speed_limit_max=200000
Permanently override default values in /etc/sysctl.conf:
$ dev.raid.speed_limit_min = 50000
$ dev.raid.speed_limit_max = 200000
Disable NCQ on all disks
for i in sd[abcde]
do
echo 1 > /sys/block/$i/device/queue_depth
done
Set read-ahead option
Get the current read-ahead value:
$ blockdev --getra /dev/mdX
Set read-ahead (in 512-byte sectors) per RAID device.
$ blockdev --setra 65536 /dev/mdX
Increase stripe cache size
Records the size (in pages per device) of the stripe cache which is used for synchronising all write operations to the array and all read operations if the array is degraded. By default, the size of the stripe cache is 256 pages and Linux uses 4096B pages. If you use 256 pages for the stripe cache and you have 10 disks, the cache would use 102564096=10MiB of RAM. Only available on RAID5 and RAID6 and boost sync performance by 3-6 times.
$ echo 4096 > /sys/block/mdX/md/stripe_cache_size