Re: RAID 5: weird size results after Grow

[Bill Davidsen <davidsen@tmr.com>]

Marko Berg wrote:
> Hi folks,
>
> I added a fourth drive to a RAID 5 array. After some complications 
> related to adding a new HD controller at the same time, and thus 
> changing some device names, I re-created the array and got it working 
> (in the sense "nothing degraded"). But size results are weird. Each 
> component partition is 320 G, does anyone have an explanation for the 
> "Used Dev Size" field value below? The 960 G total size is as it 
> should be, but in practice Linux reports the array only having 
> 625,019,608 blocks.

I don't see that number below, what command reported this?

> How can this be, even though the array should be clean with 4 active 
> devices?
>
> $  mdadm -D /dev/md0
> /dev/md0:
>        Version : 01.02.03
>  Creation Time : Sat Oct 13 01:25:26 2007
>     Raid Level : raid5
>     Array Size : 937705344 (894.27 GiB 960.21 GB)
>  Used Dev Size : 625136896 (298.09 GiB 320.07 GB)
>   Raid Devices : 4
>  Total Devices : 4
> Preferred Minor : 0
>    Persistence : Superblock is persistent
>
>    Update Time : Sat Oct 13 05:11:38 2007
>          State : clean
> Active Devices : 4
> Working Devices : 4
> Failed Devices : 0
>  Spare Devices : 0
>
>         Layout : left-symmetric
>     Chunk Size : 64K
>
>           Name : 0
>           UUID : 9bf903f8:7fc9eec1:2ff25011:37e9607b
>         Events : 2
>
>    Number   Major   Minor   RaidDevice State
>       0     253        2        0      active sync   
> /dev/VolGroup01/LogVol02
>       1       8       33        1      active sync   /dev/sdc1
>       2       8       49        2      active sync   /dev/sdd1
>       3       8       17        3      active sync   /dev/sdb1
>
>
> Results for mdadm -E <partition> on all devices appear like this one, 
> with positions changed:
>
> $ mdadm -E /dev/sdc1
> /dev/sdc1:
>          Magic : a92b4efc
>        Version : 1.2
>    Feature Map : 0x0
>     Array UUID : 9bf903f8:7fc9eec1:2ff25011:37e9607b
>           Name : 0
>  Creation Time : Sat Oct 13 01:25:26 2007
>     Raid Level : raid5
>   Raid Devices : 4
>
>  Used Dev Size : 625137010 (298.09 GiB 320.07 GB)
>     Array Size : 1875410688 (894.27 GiB 960.21 GB)
>      Used Size : 625136896 (298.09 GiB 320.07 GB)
>    Data Offset : 272 sectors
>   Super Offset : 8 sectors
>          State : clean
>    Device UUID : 9b2037fb:231a8ebf:1aaa5577:140795cc
>
>    Update Time : Sat Oct 13 10:56:02 2007
>       Checksum : c729f5a1 - correct
>         Events : 2
>
>         Layout : left-symmetric
>     Chunk Size : 64K
>
>    Array Slot : 1 (0, 1, 2, 3)
>   Array State : uUuu
>
>
> Particularly, "Used Dev Size" and "Used Size" report an amount twice 
> the size of the partition (and device). Array size is here twice the 
> actual size, even though shown correctly within parentheses.

Sectors are 512 bytes.
>
> Finally, mdstat shows the block count as it should be.
>
> $ cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4]
> md0 : active raid5 sdb1[3] sdd1[2] sdc1[1] dm-2[0]
>      937705344 blocks super 1.2 level 5, 64k chunk, algorithm 2 [4/4] 
> [UUUU]
>     unused devices: <none>
>
>
> Any suggestions on how to fix this, or what to investigate next, would 
> be appreciated!
>
I'm not sure what you're trying to "fix" here, everything you posted 
looks sane.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979