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Date: Wed, 05 Mar 2014 14:08:09 +0000
From: Karl Pielorz <kpielorz_lst@tdx.co.uk>
To: freebsd-geom@freebsd.org
Subject: HAST local read performance?
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Hi,

I have a couple of FreeBSD 10 systems I've setup HAST on - this seems to 
work well, but I've noticed the read performance of local /dev/hast/* 
devices is around half of the normal raw device?

e.g. a dd from an SSD as /dev/da0 nets around 220Mbyte/sec - the same dd 
run against the same device when setup with hast (i.e. /dev/hast/disk1) 
only nets around 110Mbyte/sec.

I realise another layer is going to affect performance (and this may just 
be the price you have to pay) but is there anything likely tunable for this?

If I fail the other node (so I'm running the test against a 'degraded 
primary') it's still as slow [as you'd kind of expect, as reads were/are 
only local]

I've setup ZFS on top of the hast devices - again this seems to work OK, 
but you can really see the performance difference when doing a pool scrub 
on hast backed devices vs. the raw ones...

-Karl