On 11/01/2011 01:45 PM, Denny Schierz wrote:
hi,
my problem is, that I loosing several terabytes ....
12 x 2TB
I create on one JBOD with 12 disks two raid 5 with one spare:
mdadm --create /dev/md7 --level=5 -x 1 --raid-disks=5
--bitmap=internal /dev/sd["cdefgh"]1
mdadm --create /dev/md8 --level=5 -x 1 --raid-disks=5
--bitmap=internal /dev/sd["ijklmn"]1
# fdisk -l /dev/md8
Disk /dev/md8: 8001.6 GB, 8001589084160 bytes
2 heads, 4 sectors/track, 1953512960 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 2097152 bytes
Disk identifier: 0x00000000
Only 8TB ...
Yes, it's correct. You have 6 disks in 1 array - 1 spare and 1 you lose
because of raid 5, so 4 * 2TB disks is 8 TB.
You would consider to build 1 array with 12 disks. With 1 spare drive
you will have 20TB RAID 5 array or you can build 22TB RAID 5 array
without a spare drive.
md8 : active raid5 sdm1[6] sdn1[5](S) sdl1[3] sdk1[2] sdj1[1] sdi1[0]
7814051840 blocks super 1.2 level 5, 512k chunk, algorithm 2 [5/4]
[UUUU_]
[>....................] recovery = 4.1% (80504380/1953512960)
finish=330.3min speed=94493K/sec
bitmap: 1/15 pages [4KB], 65536KB chunk
md7 : active raid5 sdg1[6] sdh1[5](S) sdf1[3] sde1[2] sdd1[1] sdc1[0]
7814051840 blocks super 1.2 level 5, 512k chunk, algorithm 2 [5/4]
[UUUU_]
[>....................] recovery = 4.1% (80857984/1953512960)
finish=334.0min speed=93427K/sec
bitmap: 1/15 pages [4KB], 65536KB chunk
root@iscsihead-s:~# pvscan
PV /dev/md7 lvm2 [7.28 TiB]
PV /dev/md8 lvm2 [7.28 TiB]
Total: 3 [14.78 TiB] / in use: 1 [233.81 GiB] / in no VG: 2 [14.55
TiB]
only 14TB from 20TB (2 disks are spare = 4TB) ?
that couldn't be only metadata ...
I also used --level=6 but nothing more than 8TB ...
If I create one big MD with all 12 disks and raid6, than I get 20TB
(also ~4TB metadata?)
fdisk -l /dev/md7
Disk /dev/md7: 20004.0 GB, 20003972710400 bytes
2 heads, 4 sectors/track, -1 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 5242880 bytes
Disk identifier: 0x00000000
With raid5 22TB, which seems to be better ...
But, what is the best?
To create only one big MD is something bad, I think.
On FreeBSD I have with ZFS and 2 x raidz round about 21TB.
any suggestions?
cu denny
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