[Info-vax] Raid 5 Add Disk to Raid 5 with p400 and MSA$UTIL

[gah4]

On Tuesday, April 4, 2023 at 4:04:59 PM UTC-7, Arne Vajhøj wrote:
 
(snip)

> or the RAID controller can actually handle it automatically I don't 
> know. Someone that know that RAID controller may be able to tell. 
> 
> But just to understand the basics: 
> 
> old system: 
> 
> disk1 disk2 disk3 
> blk 1 blk 2 blk 1 xor 2 
> blk 3 blk 3 xor 4 blk 4 
> blk 5 xor 6 blk 5 blk 6 
> 
> new system: 
> 
> disk1 disk2 disk3 disk4 
> blk 1 blk 2 blk 3 blk 1 xor 2 xor 3 
> blk 4 blk 5 blk 4 xor 5 xor 6 blk 6 
 
Some controller (or computer) might be able to do that.

It isn't obvious that an intermediate state is good, though,
so you probably want a full backup before starting it.

Seems to me that with appropriate checkpoint, so that it
remembers how for it has gone, and how far still to go,
that it words.  And likely when no-one else is writing.

You can generate the whole new contents of disk4,
without changing the other ones.  Some disk space,
somewhere else, for temporary use would be nice.
Copy some blocks to temporary space, record that
you did that somewhere, generate new blocks for 
those parts of the disks.  Repeat until done.

If it fails partway through, continue on based on 
the known stored temporary blocks.