Yet another reason why SATA sucks. In SCSI we can define how many blocks are exposed. So say we have a raid set like so:
root@pops:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid10 sdb1[1] sdc1[3] sdd1[2]
286875904 blocks super 1.2 32K chunks 2 near-copies [4/3] [_UUU]
bitmap: 2/3 pages [8KB], 65536KB chunk
sde is our new member and it's twice the size of the original members.
root@pops:~# lsscsi
[0:0:0:0] cd/dvd ATAPI iHAS124 C LL0B /dev/sr0
[1:0:0:0] disk ATA WDC WD1002FAEX-0 05.0 /dev/sda
[6:0:0:0] disk HITACHI HUC151414CSS600 A330 /dev/sdb
[6:0:1:0] disk HITACHI HUC151414CSS600 A330 /dev/sdc
[7:0:0:0] disk HITACHI HUC151414CSS600 A330 /dev/sdd
[7:0:1:0] disk HITACHI HUS156030VLS600 A5D0 /dev/sde
root@pops:~# sg_readcap /dev/sde
Read Capacity results:
Last logical block address=586072367 (0x22eec12f), Number of blocks=586072368
Logical block length=512 bytes
Hence:
Device size: 300069052416 bytes, 286168.1 MiB, 300.07 GB
root@pops:~# sg_readcap /dev/sdd
Read Capacity results:
Last logical block address=287140276 (0x111d69b4), Number of blocks=287140277
Logical block length=512 bytes
Hence:
Device size: 147015821824 bytes, 140205.2 MiB, 147.02 GB
I always use partitions for RAID sets just to advertise "hey, someone is probably using this", it also gives you some head room in case you start developing badblocks.
For the sake of simplicity, I want to slim down the replacement disk. I don't want those blocks available for anyone else to add another partition and make the raid member thrash due to competing IOs, so let's resize it.
root@pops:~# sg_format --resize --count=287140277 /dev/sde
HITACHI HUS156030VLS600 A5D0 peripheral_type: disk [0x0]
<< supports protection information>>
Mode Sense (block descriptor) data, prior to changes:
Number of blocks=586072368 [0x22eec130]
Block size=512 [0x200]
Resize operation seems to have been successful
and to check.
root@pops:~# sg_readcap /dev/sde
Read Capacity results:
Last logical block address=287140276 (0x111d69b4), Number of blocks=287140277
Logical block length=512 bytes
Hence:
Device size: 147015821824 bytes, 140205.2 MiB, 147.02 GB
Sweet!
Now to reuse the existing partition map from it's siblings and push it into service.
sfdisk -d /dev/sdd > part.txt
sfdisk /dev/sde < part.txt
...
and we're back in service
root@pops:~# mdadm /dev/md0 --add /dev/sde1
mdadm: added /dev/sde1
root@pops:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid10 sde1[4] sdb1[1] sdc1[3] sdd1[2]
286875904 blocks super 1.2 32K chunks 2 near-copies [4/3] [_UUU]
[>....................] recovery = 0.2% (423040/143437952) finish=28.1min speed=84608K/sec
bitmap: 2/3 pages [8KB], 65536KB chunk
unused devices:
Done.
