On Thu, 2010-06-03 at 11:49 -0500, David Dyer-Bennet wrote:
> hot spares in place, but I have the bays reserved for that use.
>
> In the latest upgrade, I added 4 2.5" hot-swap bays (which got the system
> disks out of the 3.5" hot-swap bays). I have two free, and that's the
> form-factor SSDs come in these days, so if I thought it would help I could
> add an SSD there. Have to do quite a bit of research to see which uses
> would actually benefit me, and how much. It's not obvious that either
> l2arc or zil on SSD would help my program loading, image file loading, or
> image file saving cases that much. There may be more other stuff than I
> really think of though.
It really depends on the working sets these programs deal with.
zil is useful primarily when doing lots of writes, especially lots of
writes to small files or to data scattered throughout a file. I view it
as a great solution for database acceleration, and for accelerating the
filesystems I use for hosting compilation workspaces. (In retrospect,
since by definition the results of compilation are reproducible, maybe I
should just turn off synchronous writes for build workspaces... provided
that they do not contain any modifications to the sources themselves.
I'm going to have to play with this.)
l2arc is useful for data that is read back frequently but is too large
to fit in buffer cache. I can imagine that it would be useful for
hosting storage associated with lots of programs that are called
frequently. You can think of it as a logical extension of the buffer
cache in this regard... if your working set doesn't fit in RAM, then
l2arc can prevent going back to rotating media.
All other things being equal, I'd increase RAM before I'd worry too much
about l2arc. The exception to that would be if I knew I had working
sets that couldn't possibly fit in RAM... 160GB of SSD is a *lot*
cheaper than 160GB of RAM. :-)
- Garrett
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