Neil Brown wrote:
On Thursday March 26, davidsen@xxxxxxx wrote:
I'm building a fairly aggressive machine for both a backup host for
virtual machines and spare time development platform, compile engine and
testbed both. I want to get cost effective use from an SSD unit, and I
propose to use a 32GB unit as follows: for the root filesystem, 12GB,
which should hold all the usual root things, and 16GB for swap (12GB
RAM, and I want boot and/or hibernate to happen NOW). The remaining
space I think might be used for various high impact things, and one of
those with speeding raid.
If I were to create a small raid device, raid1, made of the 4GB Ssd and
4GB of SATA space, if I made the SATA write-mostly and write-behind, and
put the journal for my raid arrays (and bitmaps?) that seems likely to
provide a significant performance gain in small storage.
Am I missing anything here? Is there an obvious drawback I'm missing?
I'd probably just put the journal on the SSD and mount my ext3
filesystem data=journal
That has a similar effect to raid1/write-behind in that data is
written to both but we only wait for the write to the SSD to
complete. But as it is done at the filesystem level - and the
filesystem has a much better idea what it is doing - you would expect
to get much more efficient results. e.g. less wasted memory, much
larger amount of data that is safe of SSD but still trickling out to
the HD.
But I think for raid in general you would benefit from having the bitmap
on SSD as well. In my dreams I also put the inodes on that SSD, and
everything runs 10x faster. Unfortunately no f/s seems to offer this.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
"You are disgraced professional losers. And by the way, give us our money back."
- Representative Earl Pomeroy, Democrat of North Dakota
on the A.I.G. executives who were paid bonuses after a federal bailout.
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