Monish Shah wrote:
Hello everyone,
I'm wondering if the following makes sense:
To configure a system for high IOPS, I want to have a zpool of 15K RPM
SAS drives. For high IOPS, I believe it is best to let ZFS stripe
them, instead of doing a raidz1 across them. Therefore, I would like
to mirror the drives for reliability.
ok, so far.
Now, I'm wondering if I can get away with using a large capacity 7200
RPM SATA drive as mirror for multiple SAS drives. For example, say I
had 3 SAS drives of 150 GB each. Could I take a 500 GB SATA drive,
partition it into 3 vdevs and use each one as a mirror for one SAS
drive? I believe this is possible.
yes, it is.
The problem is in performance. What I want is for all reads to go to
the SAS drives so that the SATA drive will only see writes. I'm
hoping that due to the copy-on-write nature of ZFS, the writes will
get bunched into sequential blocks, so write bandwidth will be good,
even on a SATA drive. But, the reads must be kept off the SATA drive.
Is there any way I can get ZFS to do that?
What sort of performance do you need?
Writes tend to be asynchronous (non-blocking) for many apps, unless your
running a database or NFS server where synchronous writes are common.
In the latter case, invest in a SSD for separate log.
Reads tend to get cached in RAM at several places in the data path, so it
is much more difficult to predict.
IMHO, today, systems which only use HDDs will not be considered high
performance in any case.
-- richard
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
