On Tue, 2010-06-08 at 15:48 -0700, David Rees wrote:

On Mon, Jun 7, 2010 at 9:54 PM, Ian Dall [off-list ref] wrote:

quoted

On Mon, 2010-06-07 at 15:14 -0400, Bill Davidsen wrote:

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Actually playing with that now. I got an Intel SATA 40GB SSD, and I am
trying various combinations of things to put on it. One thing which I
hoped would benefit was to put a f/s journal on SSD and then use the
option to push all through the journal (data=journal) in hopes that it
would then free the RAM needed for cache and thus speed operation.

Since none of that has generated the performance I hoped,

Interesting. If its the X25-V that you have, write performance is
nothing to write home about even compared to a single hard drive, let
alone a raid. By journaling data as well (as metadata), you just add
extra write overhead, possibly even a new bottleneck.

Depends on whether you are talking about small, seeky writes or large
writes.  Even the X25-V will kill any rotating drive in small seeky
writes,

Of course, low  (almost 0) seek time it the forte of SSD disks, which is
why, is seems to me, swap would be an ideal application. I may be wrong
about that, but I imagine that paging is a kind of semi random pattern.
 

quoted

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I also played with mirroring and write mostly, etc. Does provide a
general solution, at least in my tests.

Do you mean "does NOT"?

write-mostly DOES work well in my tests...

Ah! My understanding of "write-mostly" it that it is used in a mirror
(raid 0), which means that you need enough SSD to store your entire
filesystem, and the rotating disk is just redundancy. So:
capacity=capacity of SSD, speed ~= speed of SSD (until write behind
queue is full), probability of failure ~= P(Fail SSD)*P(Fail rotating
media). If the reliability of SSD is good enough (I don't know), is this
much of a win? 

Regards,
Ian

-- 
Ian Dall [off-list ref]