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I'm running an Ubuntu Linux NAS server with 4 2TB drives in software RAID 10.

I created the array during installation (with Ubuntu Server disc), but the layout is near and the chunk size is 64.

I want to change the chunk size to 256 and the layout to far. How do I do this?

Here's the output of mdstat:

root@server:~# cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid10 sde1[3] sdd1[2] sdc1[1] sdb1[0]
      3907026816 blocks 64K chunks 2 near-copies [4/4] [UUUU]

I would prefer to make the change non-destructively to save time copying the data over again, but the data is backed up, so destructive changes would be ok too.

Thank you for any help.

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Last time I looked there was no way to change this other then the obvious backup->re-create->restore method. – Zoredache Mar 1 '11 at 0:48
@Zoredache: Yeah, that's what I ended up doing. Thanks. – Andrew Mar 1 '11 at 17:29
up vote 3 down vote accepted

The only method is to destroy and re-create the array with new parameters. Neil Brown have written in his recently published road map for md:

Support reshape of RAID10 arrays.

RAID10 arrays currently cannot be reshaped at all. It is possible to convert a 'near' mode RAID10 to RAID0, but that is about all. Some real reshape is possible and should be implemented.

Whole road map is here:

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That's what I figured. Thanks for the info. – Andrew Mar 1 '11 at 17:28

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