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Re: data switchs su,sw and sunit,swidth

To: xfs@xxxxxxxxxxx
Subject: Re: data switchs su,sw and sunit,swidth
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 20 Jul 2009 13:22:21 +0200
In-reply-to: <4A626EC5.3090100@xxxxxxxxx>
Organization: it-management http://it-management.at
References: <4A626EC5.3090100@xxxxxxxxx>
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On Sonntag 19 Juli 2009 Linda Walsh wrote:
> Then, for RAID 1 (mirror) would 'sw'==1?  Would setting the  su/sw
>  value for a RAID 1 actually matter in any way?  Ie, technically --
> it would fill in numbers for OS book-keeping, but wouldn't change
> anything in terms of performance or layout, vs. 'physically' -- where
> it could change disk layout or performance?
>
> At RAID 0, I'd guess  sw==2?

Both RAID0 and RAID1 use sw=0.

> In RAID 5, would it be   sw  == #Disks-1?  So even w/6 disks, it
> still only uses 1 disk for parity and  sw == 5?

RAID5: sw = #Disks-1 ( so with 8 disks use 7)
RAID6: sw = #Disks-2 ( so with 8 disks use 6)

> I wonder what becomes a max-safe RAID 5 size? (or is the number of
> parity disks a settable option with RAID 5?)

RAID5 always only has 1 parity disk (well, technically it's not a 
physical disk, but the parity is distributed over all disks in the 
array).
Don't know what you mean by "max-safe" size. The more disks you have, 
the bigger the chance that a single disk breaks. Also, I tested with 
Areca controllers, using more than 7 disks in a single RAID array 
doesn't improve speed anymore. So I use RAID-6 for up to 8 disks, and 
make it RAID-60 for up to 16 disks (with Areca controllers).

mfg zmi
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