Skip to contentSkip to conversation

mdadm and size differences

DISCUSSION Marco De Vitis 2 participants 2 messages Nov 24, 2015 – Dec 21, 2015 MD RAID

lore
Share & tools
lore

Marco De Vitis

author
#0 lore raw

Hi,
I cannot understand a difference in size I can see on an old Debian 5.0 machine, maybe I'm just missing something obvious.

/dev/sdd is partitioned as follows, and /dev/sdf is exactly the same:

Quoted 7 lines

#>fdisk -l /dev/sdd

Disk /dev/sdd: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000901d8

Quoted 9 lines
   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1               1          24      192748+  83  Linux
/dev/sdd2              25       60801   488191252+   5  Extended
/dev/sdd5              25         632     4883728+  83  Linux
/dev/sdd6             633        2982    18876343+  83  Linux
/dev/sdd7            2983        4199     9775521   83  Linux
/dev/sdd8            4200        4807     4883728+  83  Linux
/dev/sdd9            4808        5173     2939863+  82  Linux swap / Solaris
/dev/sdd10           5174       31281   209712478+  83  Linux

You can see that sdd6 is twice the size of sdd7.
cfdisk reports sizes of around 20 GB and 10 GB:

    sdd6 -> 19329.41
    sdd7 -> 10010.17

All partitions in these two identical drives are configured as RAID 1 using mdadm, but the md devices associated to sdd6/sdf6 and sdd7/sdf7 are both reported to be 10 GB in size, as can be seen from the mdadm output below.

Why?

Thanks for any info.

Quoted 51 lines

#>mdadm -vv --detail /dev/md2
/dev/md2:

        Version : 00.90

Creation Time : Thu Feb 22 16:18:11 2007
Raid Level : raid1
Array Size : 9767424 (9.31 GiB 10.00 GB)
Used Dev Size : 9767424 (9.31 GiB 10.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 2
Persistence : Superblock is persistent

Update Time : Mon Nov 23 14:19:23 2015
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

UUID : 5582dad7:7ac89883:0c2b9e1d:5009dd35
Events : 0.69228

Number Major Minor RaidDevice State
0 8 54 0 active sync /dev/sdd6
1 8 86 1 active sync /dev/sdf6

#>mdadm -vv --detail /dev/md3
/dev/md3:

        Version : 00.90

Creation Time : Thu Feb 22 16:18:54 2007
Raid Level : raid1
Array Size : 9767424 (9.31 GiB 10.00 GB)
Used Dev Size : 9767424 (9.31 GiB 10.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 3
Persistence : Superblock is persistent

Update Time : Mon Nov 23 14:19:27 2015
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

UUID : e44836cf:6340f7fa:52fb3562:a78d4dbb
Events : 0.187630

Number Major Minor RaidDevice State
0 8 55 0 active sync /dev/sdd7
1 8 87 1 active sync /dev/sdf7

Signature · 2 lines
Ciao,
  Marco.
#1 lore raw
Quoted 3 lines · Marco De Vitis

Hi,
I cannot understand a difference in size I can see on an old Debian 5.0 machine, maybe I'm just missing something obvious.

...

Quoted 6 lines

You can see that sdd6 is twice the size of sdd7.
cfdisk reports sizes of around 20 GB and 10 GB:

     sdd6 -> 19329.41
     sdd7 -> 10010.17
Quoted 6 lines

All partitions in these two identical drives are configured as RAID 1 using mdadm, but the md devices associated to sdd6/sdf6 and sdd7/sdf7 are both reported to be 10 GB in size, as can be seen from the mdadm output below.

Why?

Probably because the arrays aren't using the whole partition. e.g. if you have a RAID! comprised of 2 1GB partitions, then you fail one partition and had a 2GB partition as a spare and let it rebuild. Then fail the other 1GB partition and add a 3GB partition as a spare and let it rebuild.
Then you will have a 1GB RAID made from 2 partitions, a 2GB partition and a 3GB partition.

If you want to resize the RAID! to use all the available space, then use the command
mdadm --grow /dev/md2 --size=max

You might then need to resize and filesystem you have in that array.

NeilBrown

Quoted 63 lines

Thanks for any info.

Quoted 51 lines

#>mdadm -vv --detail /dev/md2
/dev/md2:

        Version : 00.90

Creation Time : Thu Feb 22 16:18:11 2007
Raid Level : raid1
Array Size : 9767424 (9.31 GiB 10.00 GB)
Used Dev Size : 9767424 (9.31 GiB 10.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 2
Persistence : Superblock is persistent

Update Time : Mon Nov 23 14:19:23 2015
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

UUID : 5582dad7:7ac89883:0c2b9e1d:5009dd35
Events : 0.69228

Number Major Minor RaidDevice State
0 8 54 0 active sync /dev/sdd6
1 8 86 1 active sync /dev/sdf6

#>mdadm -vv --detail /dev/md3
/dev/md3:

        Version : 00.90

Creation Time : Thu Feb 22 16:18:54 2007
Raid Level : raid1
Array Size : 9767424 (9.31 GiB 10.00 GB)
Used Dev Size : 9767424 (9.31 GiB 10.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 3
Persistence : Superblock is persistent

Update Time : Mon Nov 23 14:19:27 2015
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

UUID : e44836cf:6340f7fa:52fb3562:a78d4dbb
Events : 0.187630

Number Major Minor RaidDevice State
0 8 55 0 active sync /dev/sdd7
1 8 87 1 active sync /dev/sdf7

Signature · 7 lines
Ciao,
   Marco.

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html