On Apr 19, 2013, at 4:40 AM, Andrew Evdokimov <[email protected]> wrote:
> Hi Paul,
>
> On 18.04.2013 22:41, Paul B. Henson wrote:
>> I'm just about ready to deploy the home storage server I've been working
>> on for a while, and am trying to decide what do about swap. The box has
>> 12 3TB drives configured as two 6 disk raidz2 vdevs and will have about
>> 300G of L2ARC. Right now it has 32G of memory. I ended up deciding to
>> have a separate virtualization server so this one is pretty much only
>> going to do file service via CIFS/NFS.
>
> you need a 32G swap device on any drive you like just to satisfy swap
> allocation requirements coming from applications.
Not likely. Measure it before using generalizations.
# echo ::memstat | mdb -k
Page Summary Pages MB %Tot
------------ ---------------- ---------------- ----
Kernel 512397 2001 51%
ZFS File Data 339851 1327 34%
Anon 48038 187 5%
Exec and libs 3156 12 0%
Page cache 7057 27 1%
Free (cachelist) 4257 16 0%
Free (freelist) 98792 385 10%
Total 1013548 3959
Physical 1013547 3959
So this box needs 187 MB of swap to back the anonymous pages.
note: Bob's workload, much like Bob, is special in so many ways :-)
-- richard
> It's very unlikely that your system will be responsive if paging or swapping
> will start regardless of type of swap device (SSD or HDD), thus there is no
> need to have a swap size larger than a RAM and no need to place swap on a
> faster drives. It's also very unlikely that any single I/O will be issued to
> a swap device if you don't tune your applications to consume more RAM that is
> available, thus again there is no need to place swap on expensive SSDs.
>
> WBR,
> Andrew
>
>
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