Goswin von Brederlow wrote:
Keld Jørn Simonsen <keld@xxxxxxxxxx> writes:
On Sat, Jan 09, 2010 at 09:53:11AM -0800, Wil Reichert wrote:
Has anyone ever tried putting an SSD and a mechanical disc in RAID 1
using write-mostly? The goal would be to extol the speed & latency
virtues of an SSD while retaining the integrity of the traditional
storage. Would this setup even work as I expect it to?
I think you are better served by trying out RAID10 in the far or offset
layouts. RAID1 would per se not gain from the low latency times of
SSD. RAID1 should function the same with hard disk as with SSD,
and with hard disk it would not make sense to multiplex reading
of a file, as skipping and reading a block essentially takes the same
time.
Best regards
Keld
With raid10 in the far or offset layout every (large) read and write
would always access both the SSD and rotating disk. That would make
every operation wait for the rotating disk to seek.
I think his initial idea of raid1 is verry good. With write-mostly all
reads should come from the fast SSD. I would also add write-behind.
That way writes will not wait for the rotating disk and get the full
SSD speed as well.
I had an SSD waiting to be deployed, and I tried putting a journal on it
and using a mount with data=journal. Supposedly when the data is written
to the journal the write will be "complete" and effective write speed
for many small random writes will be higher. I don't have the results
handy, but they were not so great that I went out and got another SDD.
--
Bill Davidsen <davidsen@xxxxxxx>
"We can't solve today's problems by using the same thinking we
used in creating them." - Einstein
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