From: "H. Peter Anvin" <hpa@zytor.com>
To: Guy <bugzilla@watkins-home.com>
Cc: 'Jim Paris' <jim@jtan.com>, 'Neil Brown' <neilb@cse.unsw.edu.au>,
linux-raid@vger.kernel.org
Subject: Re: RAID-6: help wanted
Date: Fri, 29 Oct 2004 13:32:16 -0700 [thread overview]
Message-ID: <4182A8D0.6050000@zytor.com> (raw)
In-Reply-To: <200410292028.i9TKS6N14580@www.watkins-home.com>
Guy wrote:
> Could you translate this into English?
> P' = P + D_n + D_n'
> Q' = Q + g^n * D_n + g^n * D_n'
>
> I understand this much:
> P =old parity
> D_n =old data block(s)
> P' =new parity
> D_n' =new data block(s)
>
> But is "+" = xor?
>
> I am lost on this one:
> Q' = Q + g^n * D_n + g^n * D_n'
>
> With the parity (xor) it can be done by the bit, so an example is easy.
> Can Q be done by the bit, and if so, could you give an example?
>
> If it takes more than 10 minutes, just tell me it is magic! :)
See my paper on the subject:
http://www.kernel.org/pub/linux/kernel/people/hpa/raid6.pdf
> Also, on a related subject....
> I have a 14 disk RAID5 with 1 spare.
> Once RAID6 seems safe and stable I had hoped to convert to a 15 disk RAID6.
> Is 15 disks too much for RAID6?
> Any idea what a reasonable limit would be?
>
The limit is 27 disks total, it's imposed by the md system rather than RAID-6;
RAID-6's inherent limit is 254+2 (see, again, the paper.)
-hpa
next prev parent reply other threads:[~2004-10-29 20:32 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-23 23:46 RAID-6: help wanted H. Peter Anvin
2004-10-24 5:26 ` Brad Campbell
2004-10-24 6:46 ` Jim Paris
[not found] ` <417B546C.3050706@zytor.com>
2004-10-24 7:09 ` H. Peter Anvin
2004-10-24 7:17 ` H. Peter Anvin
2004-10-24 7:18 ` Brad Campbell
2004-10-25 5:41 ` Neil Brown
2004-10-25 6:20 ` Jim Paris
2004-10-25 6:24 ` Neil Brown
2004-10-25 6:33 ` Jim Paris
2004-10-25 14:23 ` H. Peter Anvin
2004-10-27 3:38 ` Neil Brown
2004-10-27 5:23 ` H. Peter Anvin
2004-10-27 6:00 ` Jim Paris
2004-10-27 6:03 ` H. Peter Anvin
2004-10-28 1:17 ` H. Peter Anvin
2004-10-28 16:00 ` Jim Paris
2004-10-28 17:48 ` H. Peter Anvin
2004-10-28 17:49 ` H. Peter Anvin
2004-10-29 0:43 ` Neil Brown
2004-10-29 11:48 ` Jim Paris
2004-10-29 12:56 ` Guy
2004-10-29 18:15 ` Jim Paris
2004-10-29 19:04 ` H. Peter Anvin
2004-10-29 19:21 ` Jim Paris
2004-10-29 19:33 ` H. Peter Anvin
2004-10-29 20:28 ` Guy
2004-10-29 20:32 ` H. Peter Anvin [this message]
2004-10-29 21:21 ` Guy
2004-10-29 21:33 ` H. Peter Anvin
2004-10-29 12:29 ` Guy
2004-10-27 5:56 ` H. Peter Anvin
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