Re: [Scst-devel] Honoring SYNC requests in combination with ZFS

[Sietse v. Z. <si...@wi...>]

I don't believe so. ZFS has its own caching mechanism, so this setting will not have any effect, just like o_direct. The effect is achieved by the zfs set sync=always setting for the filesystem or zvol..

-Sietse

-----Original Message-----
From: Vladislav Bolkhovitin [mailto:vs...@vl...] 
Sent: Friday, February 28, 2014 22:50
To: Sietse van Zanen
Cc: Thijs Cramer; scs...@li...
Subject: Re: [Scst-devel] Honoring SYNC requests in combination with ZFS

Sietse van Zanen, on 02/28/2014 02:57 AM wrote:
> You have to do 3 things.
> 
> 
> 
> 1. Set nv_cache to 0 on the scst side

You mean write_through in 1 here, I believe.

Vlad

> 2. zfs set sync=always for the filesystem or zvol you have the file on.
> 
> 3. Use ZIL or your performance will be terrible, definitely with SATA
> 
> 
> 
> -Sietse
> 
> 
> 
> ________________________________
> From: Thijs Cramer [thi...@gm...]
> Sent: Tuesday, February 25, 2014 08:59
> To: scs...@li...
> Subject: [Scst-devel] Honoring SYNC requests in combination with ZFS
> 
> Guys,
> 
> Is there a definitive answer on whether we can use the fileio handler in combination with ZFSonLinux?
> I'm seeing extreme performance statistics > 18.000 IOPS over iSCSI when using ZFSonLinx on 4*4TB drives with sync=standard. The disks are exported over iSCSI through a ZVOL and I've defined a fileio handler in SCST. The iSCSI volume is exported to an ESXi cluster.
> 
> I think this means that SCST doesn't honor the SYNC requests from ESXi.
> 
> I know the linux page cache is involved when using the fileio handler, but i thought sync requests would still be honored? Am i mistaking?
> 
> - Thijs
> 
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