v slow raid resync

[stigger]

OK todays problem.

I have a HP N54L Microserver running centos 6.5.

In this box I have a 3x2TB disk raid 5 array, which I am in the process of extending to a 4x2TB raid 5 array.

I've added the new disk --> mdadm --add /dev/md0 /dev/sdb

And grown the array --> mdadm --grow /dev/md0 --raid-devices=4

Now the problem the resync speed is v slow, it refuses to rise above 5MB, in general it sits at 4M.

from looking at glances it would appear that writing to the new disk is the bottle neck, /dev/sdb is the new disk.

Disk I/O In/s Out/s
md0 0 0
sda1 0 0
sda2 0 1K
sdb1 3.92M 0
sdc1 24.2M 54.7M
sdd1 11.2M 54.7M
sde1 16.3M 54.7M

I partitiioned the disk with --> parted -a optimal /dev/sdb

[root@nas ~]# parted -a optimal /dev/sdb
GNU Parted 2.1
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Model: ATA ST2000DM001-1E61 (scsi)
Disk /dev/sdb: 2000GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos

Number Start End Size Type File system Flags
1 1049kB 2000GB 2000GB primary ntfs raid

There is no ntfs filesystem on the disk, I've still not worked out how to remove that flag.

I've followed the article here -->

http://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html

to attempt to speed it up but no joy.

Any Ideas what I've done wrong?

parted output

[root@nas ~]# parted -l
Model: ATA ST31000528AS (scsi)
Disk /dev/sda: 1000GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number Start End Size Type File system Flags
1 1049kB 525MB 524MB primary ext4 boot
2 525MB 1000GB 1000GB primary lvm


Model: ATA ST2000DM001-1E61 (scsi)
Disk /dev/sdb: 2000GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos

Number Start End Size Type File system Flags
1 1049kB 2000GB 2000GB primary ntfs raid


Model: ATA ST2000DM001-9YN1 (scsi)
Disk /dev/sdc: 2000GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos

Number Start End Size Type File system Flags
1 1049kB 2000GB 2000GB primary raid


Model: ATA WDC WD25EZRS-00J (scsi)
Disk /dev/sdd: 2500GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos

Number Start End Size Type File system Flags
1 1049kB 2000GB 2000GB primary ntfs raid


Model: ATA ST2000DL001-9VT1 (scsi)
Disk /dev/sde: 2000GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos

Number Start End Size Type File system Flags
1 1049kB 2000GB 2000GB primary raid

 

[stigger]

OK there's definitly something wrong with sdb...

Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
sdb 3.26 1005.29 0.03 8.06 0.01 3.96 1004.23 3.97 485.04 122.39 99.08
sdc 1512.55 1014.82 22.23 8.53 6.00 4.00 665.20 6.33 205.71 4.58 14.08
sda 5.37 5.36 1.51 1.94 0.04 0.03 40.56 0.17 48.75 5.61 1.93
sdd 1521.43 1014.82 13.44 8.38 6.00 4.00 937.55 17.97 823.46 9.82 21.43
sde 1520.76 1014.95 14.01 8.41 6.00 4.00 912.80 11.94 532.72 7.89 17.7

3.96 MB is 100%

It's a replacement disk from seagate only 80 odd hours in smart...

so why would a SATA disk max out a 4MB/S