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Re: swidth in RAID

To: stan@xxxxxxxxxxxxxxxxx
Subject: Re: swidth in RAID
From: aurfalien <aurfalien@xxxxxxxxx>
Date: Sun, 30 Jun 2013 15:36:06 -0700
Cc: xfs@xxxxxxxxxxx
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On Jun 30, 2013, at 2:42 PM, Stan Hoeppner wrote:

> On 6/30/2013 1:43 PM, aurfalien wrote:
> 
>> I understand swidth should = #data disks.
> 
> No.  "swidth" is a byte value specifying the number of 512 byte blocks
> in the data stripe.
> 
> "sw" is #data disks.
> 
>> And the docs say for RAID 6 of 8 disks, that means 6.
>> 
>> But parity is distributed and you actually have 8 disks/spindles working for 
>> you and a bit of parity on each.
>> 
>> So shouldn't swidth equal disks in raid when its concerning distributed 
>> parity raid?
> 
> No.  Lets try visual aids.
> 
> Set 8 coffee cups (disk drives) on a table.  Grab a bag of m&m's.
> Separate 24 blues (data) and 8 reds (parity).

But are the cups 8oz, 16oz or smaller/larger?

Ceramic, plastic, glass, etc...?

Actually I really enjoyed the visual aid, many many thanks.

- aurf

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