Hello Massimo,
Massimo Maggi wrote (ao):
SSDs have low latency but a high price per GB,
Traditional hard disks have high latency, but high sequential read/write
speed and low price per GB.
Is possibile to use a SSD for metadata, which requires many seeks and is
relatively small, in a special RAID mode with a traditional hard disk
for the extents of the real data?
A cheap but performant SSD (maybe 32 GB) + a big and fast HD (maybe 1.5
TB, or two in RAID0 - 3TB ), wouldn't create an array much cheaper than
a ssd-only array of the same size, and much faster (in
not-only-sequential workload) than one or two traditional HDs in RAID0?
Would it work?
If you talk RAID0 (eg no redundancy), you could RAID0 one or several
traditional disks, and use the SSD as a journal device. That would be
ext3/4 only btw.
With mdadm you could create a RAID1 and use --write-mostly:
-W, --write-mostly
subsequent devices listed in a --build, --create, or --add com-
mand will be flagged as 'write-mostly'. This is valid for RAID1
only and means that the 'md' driver will avoid reading from
these devices if at all possible. This can be useful if mirror-
ing over a slow link.
Where the 'slow link' would be the traditional disk. But this is raid1 and
doesn't help in your case (but couldn't resist the need to mention it :-)
Sander
--
Humilis IT Services and Solutions
http://www.humilis.net
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