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Re: [dm-devel] [PATCH v3 0/8] dm-raid (raid456) target




On Jan 9, 2011, at 6:37 PM, NeilBrown wrote:

Also:

3:	<#raid_devs> <meta_dev1> <dev1> .. <meta_devN> <devN>

This doesn't allow offsets into the various devices like dm-stripe,
dm-linear, dm-raid1 all do.

This is a conscious choice.  The offset was discarded because it is
unneeded.

Famous last words!!!

:)


When reshaping a RAID5/6 to change the chunk size or layout, or when
converting an N drive RAID5 to N+1 drive RAID6, it makes it a lot easier if you can can change the data offset at the same time. Then you don't have to keep backing up data. md cannot do this yet but I hope to add the code soon and because 'data_offset' is a distinct value it is conceptually easy to do.
If 'data_offset' is assumed to be zero, then it isn't.

I guess I don't understand this part. Why would you need to change the data offset? Especially the offset as it relates to the individual drives?

But I don't know to what extent you are planning on supporting reshaping of
arrays....

I don't see a reason why this can't be completely supported...

 brassow


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