Re: RFC - new raid superblock layout for md driver

From: Steve Pratt (slpratt@us.ibm.com)
Date: Wed Nov 20 2002 - 10:55:55 EST


Neil Brown wrote;

>I would like to propose a new layout, and to receive comment on it..

>/* constant this-device information - 64 bytes */
>u64 address of superblock in device
>u32 number of this device in array /* constant over reconfigurations
    */

 Does this mean that there can be holes in the numbering for disks that die
    and are replaced?

>u32 device_uuid[4]
>u32 pad3[9]

>/* array state information - 64 bytes */
>u32 utime
>u32 state /* clean, resync-in-progress */
>u32 sb_csum

 These next 2 fields are not 64 bit aligned. Either rearrange or add
    padding.

>u64 events
>u64 resync-position /* flag in state if this is valid)
>u32 number of devices
>u32 pad2[8]

>Other features:
>A feature map instead of a minor version number.

Good.

>64 bit component device size field.

Size in sectors not blocks please.

>no "minor" field but a textual "name" field instead.

Ok, I assume that there will be some way for userspace to query the minor
   which gets dynamically assigned when the array is started.

>address of superblock in superblock to avoid misidentifying superblock.
   e.g. is it >in a partition or a whole device.

Really needed this.

>The interpretation of the 'name' field would be up to the user-space
>tools and the system administrator.

Yes, so let's leave this out of this discussion.

EVMS 2.0 with full user-space discovery should be able to support the new
superblock format without any problems. We would like to work together on
this new format.

Keep up the good work, Steve

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