Problems formatting MDADM array

jbruyet · 11-05-2012, 12:03 PM

Hey all, I just created a 2TB RAID10 array using four 1TB hard disks (my first ever attempt). Everything went fine until I tried formatting the array. When I run:

Code:

mkfs -t ext4 /dev/md10

I get the following warning:

Code:

root@MAbackup:/home/jobee# mkfs -t ext4 /dev/md10
mke2fs 1.41.12 (17-May-2010)
/dev/md10 alignment is offset by 512 bytes.
This may result in very poor performance, (re)-partitioning suggested.

Re-partitioning didn't help at all so I did some Googling and saw that changing the starting sector so that it's evenly divisible by 8 should fix it. Well, when I try to change the beginning sector I get the following error:

Code:

Command (m for help): x

Expert command (m for help): b
Partition number (1-4): 1
Partition 1 has no data area

Expert command (m for help):

I have no idea what I'm doing and the few tutorials I've watched haven't been helpful. Can anyone point me to a tutorial that will help me get this working? I think my problem is with fdisk but could it be with mdadm?

Thanks,

Joe B

jbruyet · 11-05-2012, 12:09 PM

Here's something else I just found:

Code:

root@MAbackup:/home/jobee# fdisk /dev/md10

The device presents a logical sector size that is smaller than
the physical sector size. Aligning to a physical sector (or optimal
I/O) size boundary is recommended, or performance may be impacted.

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help):

I need the 2TB size because I'm running a backup for another device and I need to match its size with my array. Have I hit a size limitation?

Thanks,

Joe B

jbruyet · 11-07-2012, 01:19 PM

Ok, well, I tried another recommendation:

Code:

root@MAbackup:/home/jobee# echo "128,," | sfdisk -uS /dev/md10

And now I get an even larger offset when I run mkfs:

Code:

root@MAbackup:/home/jobee# mkfs -t ext4 /dev/md10p1
mke2fs 1.41.12 (17-May-2010)
/dev/md10p1 alignment is offset by 459264 bytes.
This may result in very poor performance, (re)-partitioning suggested.

I see too that my original md10 has been changed to md10p1. Hmmm. Then I tried using "512" to replace the "128" in the sfdisk command and that drops me to an offset of 262656 bytes. I've even used a spreadsheet to try to find something that would give me a 0 byte offset but no joy. I thought I was close until I saw this error message:

Code:

sfdisk: I don't like these partitions - nothing changed.
(If you really want this, use the --force option.)

Yes, I'm stumbling around but I need to get this working. Am I going to have to live with the 512 byte offset? How much of a performance hit will I take? At this point I'll take pretty much any ideas, suggestions or recommendations.

Thanks,

Joe B