Using an SSD as swap?

[tmetro-blu-5a1Jt6qxUNc at public.gmane.org (Tom Metro)]

Robert Krawitz wrote:
> Daniel Feenberg wrote:
>> How about battery backed Ram?
>>
>>    http://www.anandtech.com/show/1742
>>    http://techreport.com/articles.x/16255
> 
> The issue is simply that my laptop is RAM-limited and it's maxed out.
> If I could install 8 or 16 GB in it, I wouldn't be having this
> discussion.

The articles above refer to devices that have a SATA drive interface.
They just happen to use DRAM as the storage medium instead of Flash memory.

Unfortunately both articles are a tad old (2005, 2009). The Product
mentioned in the first fits into a PCI slot (I think just for power, as
it too has a SATA interface) and has been discontinued. The second is
built into a 5.25" drive chassis (like a CD drive) and uses desktop
style RAM modules. So neither is applicable to a laptop application.

In theory using DRAM has a big speed win. The 2nd device above even has
2 SATA ports so you can split the drive and do RAID0 across two SATA
ports for increased performance.

Now that SSDs are starting to be used as file cache/buffers on high
performance filers (I believe ZFS has a mode specifically to take
advantage of an SSD buffer), I would think these DRAM drives would be
common.

What you're looking for is a 2.5" drive form factor, SATA interface, and
the ability to use SODIMMs for storage. And like you said, for a swap or
RAM disk application, you can forgo the complexity of a battery backup.

The same manufacturer sells a 2.5" SSD that uses SDHC cards for storage.

http://www.amamax.com/acaan2safldi.html

If you could find SDHC cards or perhaps a CF form-factor card that was
(S or D)RAM instead of Flash, you could probably piece together a
solution. But I don't see any evidence that such cards exist.

Also, if you read through the 2nd article to the benchmarks, you'll see
that the Intel X25-E Extreme SSD outperformed the ACard DRAM drive on
some benchmarks, despite the latter having much better theoretical
bandwidth. The reviewer attributed this to a superior drive controller
in the Intel drive. This in part addresses your question about NCQ.
Without running benchmarks, though, it would be hard to say whether the
extra cost is justified. Any SS storage is likely to be a substantial
improvement over swapping to rotating media.

 -Tom

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
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