Re: Using high speed swap to improve performance?

On Fri, Apr 2, 2010 at 1:15 PM, Christiaan Willemsen
<cwillemsen(at)technocon(dot)com> wrote:
> Hi there,
>
> About a year ago we setup a machine with sixteen 15k disk spindles on
> Solaris using ZFS. Now that Oracle has taken Sun, and is closing up Solaris,
> we want to move away (we are more familiar with Linux anyway).
>
> So the plan is to move to Linux and put the data on a SAN using iSCSI (two
> or four network interfaces). This however leaves us with with 16 very nice
> disks dooing nothing. Sound like a wast of time. If we were to use Solaris,
> ZFS would have a solution: use it as L2ARC. But there is no Linux filesystem
> with those features (ZFS on fuse it not really an option).
>
> So I was thinking: Why not make a big fat array using 14 disks (raid 1, 10
> or 5), and make this a big and fast swap disk. Latency will be lower than
> the SAN can provide, and throughput will also be better, and it will relief
> the SAN from a lot of read iops.
>
> So I could create a 1TB swap disk, and put it onto the OS next to the 64GB
> of memory. Then I can set Postgres to use more than the RAM size so it will
> start swapping. It would appear to postgres that the complete database will
> fit into memory. The question is: will this do any good? And if so: what
> will happen?

I'd make a couple of RAID-10s out of it and use them for highly used
tables and / or indexes etc...