On Monday October 9, markryde@xxxxxxxxx wrote:
> Hello,
>
> I wonder what is the "type-0.90.0" superblock and "md-1" superblocks
> of md and what is the differnce between them? Is it merely
> some version of kernel md driver ?
Two different formats for the metadata describing the array.
I usually refer to them as v0.90 and v1.
Some of the differences are subtle. Some of the less subtle are:
- v0.90 is limited to 28 components in an array. v1 allows > 256.
- v1 supports restarting driver recovery that was interrupted by
a clean shutdown. v0.90 doesn't.
- v1 can easily be moved between machines with different byte-order.
v0.90 needs explicit conversion.
- v0.90 records a small number to identify the array. v1 stores a
textual name.
- v0.90 can be used with 'in kernel autodetect' (i.e. partition type
0xfd). v1 cannot (I consider this an improvement :-)
- v0.90 can get confused if a partition and a whole device are
aligned so that the superblock would be at exactly the same
location. v1 avoids this confusion.
> In case it is so - is there a way to know which is
> the version of the md superblocks which is in use in my kernel ?
>
2.6 kernels support both, though there have been a number of v1
specific bugs slowly being ironed out over the months. From 2.6.18 I
consider v1 perfectly stable for regular use. In earlier kernels it
was quite usable but there were a few minor bugs.
mdadm create v0.90 by default, though the default can be changed in
/etc/mdadm.conf.
> I see that in drivers/md/md.c
> there is an array of super_type with 2 elements,
> the name of the first is "0.90.0",and the name of the second
> is "md-1".
>
> when running :
> mdadm --detail /dev/md0
> I see:
> /dev/md0:
> Version : 00.90.01
> ..
>
> is this "Version" field is the superblock type ?
The "01" at the end is really a version number for the driver rather
than a version number for the metadata (aka superblock) - md version
numbers were not thought out probably and so are confusing.
Yes, the "Version" reported by mdadm --detail reflects the superblock
type.
NeilBrown
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