Choosing the superblock format for Linux's software RAID
February 8, 2012
Linux's software RAID implementation stores metadata about the RAID
device in each physical device involved in the RAID, in what
(Even if you don't actively make a decision,
In my opinion, at the moment there are three sensible options to choose from: the 0.90 format and then two variants of the 'version-1' metadata format.
(You can see what format your current RAID arrays are using by looking
Where the superblock goes is potentially important for RAID-1 arrays. A RAID-1 array with the superblock at the end can relatively easily have whatever filesystem it contains mounted read-only without the RAID running, because the filesystem will start at the start of the underlying raw partitions; this can be important sometimes. A RAID-1 array with the superblock at or near the start of the underlying partitions can't have the raw partitions used this way, because you have to look somewhat beyond the start of the raw partition to see the filesystem.
(Some versions of
If you want to use a modern format and are going to directly use the
RAID-1 array for a filesystem, I would use 1.0 format (this is what
I've done for my new
(LVM physical volumes have their own metadata, which normally goes at
the start of the 'raw' partition that LVM is using but which can be
replicated to the end as well. See
As far as I know you can't change the superblock format of an array after it has been created, at least not without destroying it and recreating it. You can sort of do this without an extra disk with sufficient work, but really you want to get it right at creation time.
PS: note that in theory you can use
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