HAST local read performance?

[Mark Felder]

On Wed, Mar 5, 2014, at 8:08, Karl Pielorz wrote:
> 
> 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...
> 

Which HAST replication mode are you using? Fullsync? Do you have atime
enabled on that filesystem? I'd expect it to act like a local disk
without any significant penalties unless you're doing writes and they're
waiting to be synced before the next read.