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List:       freebsd-hackers
Subject:    Re: SCSI Bus redundancy...
From:       Terry Lambert <tlambert () primenet ! com>
Date:       1998-02-28 23:24:30
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> > > I think Julian's SLICE code has something in that direction.  DPT
> > > supports INCREASING the size of a RAID-5 array by adding drives.
> > 
> > How can that work?
>
> Something like 
> 	- read N RAID blocks from K disks
> 	- compute new checksum for K+1 disks and write as less number
>         of RAID blocks but each one of bigger size (K+1/K times)
>       - add empty blocks at the end of RAID in the added space
> 
> What am I wondering is why nobody did that before ? It's so boring
> to rebuild the whole RAID if all you want is to add or remove a disk.

You would have to remember to grab the blocks to be relocated with
the same O(n) randomness as their allocation.  8-).

This is exactly analogous to the FFS extension problem discussed
in another thread.

Why hasn't it been done?  Maybe too many programmers and too few
computer scientists?  8-).  It's a math problem... ;-).


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.

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