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DragonFly users List (threaded) for 2013-03
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Re: How to do a software based RAID 1+0?

From: Chris Turner <c.turner@xxxxxxxxxxxxxxxxxxx>
Date: Sat, 30 Mar 2013 12:30:49 -0500

On 03/17/13 20:13, Constantine A. Murenin wrote:

> If you're dealing with regular platter-based HDDs, would you
> nonetheless configure the second HDD (which is the target of the
> `hammer mirror-stream`) as swapcache?  Wouldn't it potentially make
> the performance much worse?

I think for this scenario people tend to be doing:

1) System disk (OS only or OS+packages) on SSD with giant swap partition
    for swapcache
2) Pair of data drives (primary / secondary) with mirror-stream between
    primary & secondary

You can rate-limit the mirror-stream if you want to reduce the mirroring

In the 2-disk scenario you mention, swapcache on either drive will
be reducing performance since the swapcache is in the 'critical path'
with respect to mirrored data - although when coupled with bandwidth
limiting you might be able to reduce that impact and keep the second
platter more 'available' for your swapcache.

Obviously, compared to 'real raid' this is a best-effort failover
since there can be some delay, but you'll generally
get 'just about everything' which is probably fine for many



- Chris

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