[OpenIndiana-discuss] SSD as a dedicated swap device

[Andrew Gabriel]

On 11/12/2015 20:45, Ian Collins wrote:
> Reginald Beardsley via openindiana-discuss wrote:
>> I have only occasional need to  run problems larger than main memory
> > (16 GB at present), so I can't justify replacing all the DRAM for an
> > infrequent need. The drop in SSD prices has me contemplating adding
> > a 128 GB SSD as a swap device. The SSD latency and IOPS specs look
> > as if they might be a useful compromise.
> >
> > Does anyone have any experience with this? The sort of jobs I'm
> > interested in are batch processes that take several hours, not
> > interactive tasks.
>
> Even an SSD will be way slower than RAM.

Yep

>> At present rpool is a ZFS 3 way  mirror. It's become a bit unclear to
> > me if it is still possible to control the swap device independently
> > of other parts of the system contained in rpool. Back in SunOS 4.x
> > days I ran with a pair of swap partitions spread across two disks
> > which got me twice the performance on large array operations.
>
> I don't think you can add the drive as a drive, but you could create a 
> pool with a single volume on on it and add that volume with "swap -a 
> /dev/zvol/dsk/<pool>/<volume>.
>

Adding a swap partition or slice from a drive worked just fine last time 
I did it. You don't have to swap on ZFS (and there have been some good 
reasons not to in the past).
I would expect using a whole drive (the p0 device) would also work, 
although the danger with doing that is that many tools which don't find 
FDISK or GPT partitioning on the disk will assume the disk is unused.

-- 
Andrew