[zfs-discuss] ZFS on RAM optimizations questions

Durval Menezes durval.menezes at gmail.com
Fri Oct 18 21:24:38 EDT 2013


Hi Maxpil,

I think you are just subjecting ZFS to inhuman and cruel treatment ;-)
Seriously, ZFS was not made for that.

Just for curiosity's sake, have you tried measuring performance with a more
"traditional" ramdisk file system like tmpfs or even zram?

Cheers,
-- 
   Durval.



On Fri, Oct 18, 2013 at 9:35 PM, <maxpil at gmail.com> wrote:

> Hello,
>
> I am running ZFS on RAM disk using brd module (/dev/ram0). The RAM disk is
> 150GB.
>
> Here is my config:
>
> zpool create -O atime=off  -O dedup=on  -O sync=disabled mypool /dev/ram0
>
> the performance I am getting is about 186MB/s sequential write.  I was
> thinking I should be getting more than this writing to RAM with ZIL
> disabled.
>
> I have also tried this config:
>
> zpool create -O atime=off  -O dedup=on  -O  primarycache=none -O
>  secondarycache=none  -O sync=disabled mypool /dev/ram0
>
> This config resulted in much worse performance.
>
>
> - Should primarycache/secondary cache be disabled on RAM disk? If so, why
> did I see worse performance with them disabled
> - what other RAM disk block devices I can try in Linux? I am aware of zram
> and rapiddisk
> - what module options would be helpful to optimize for RAM disk?
> - should I limit ARC, and if so how much?
> - is there still a per VDEV IOPS limit? I only have 1 RAM device in the
> pool that is 150GB would it make sense to do a stripe across several RAM
> disks?
>
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