On Fri, 9 Oct 2009, tak ar wrote:
Hi! I bought x4270 servers for (write heavy) mail server. And
waiting for delivery. That have two Intel SSD X25-E(for ZIL) and
HDDs. x4270 servers have hardware RAID card based on Adaptec's RAID
5805 adapter, which has 256MB BBWC.
SSD has write cache and RAID card also has BBWC. When set write-back
on BBWC and enable SSD's write cache on RAID card, ZFS can flash the
BBWC and SSD's write cache too?
The BBWC is much more useful than the write cache on the X25-E since
the X25-E's write cache is volatile and therefore may cause harm to
your data. According to reports I have seen, the X25-E write IOPS
reduces by a factor of five when its write cache is disabled.
When the answer is no, should I set disable SSD's write cache? I
think disabled write cache reduce the usable lifetime of SSD.
Because wear-leveling on SSD is not applied.
I find this difficult to believe. I doubt that it disables the
wear-leveling algorithm since then the product might only survive for
hours or days before burn-out. There may be more low-level writes
though which could result in quicker wear.
And one more question. Which RAID function should I use hardware and
ZFS?
Use ZFS for the RAID if you can. Use the BBWC to reduce the latency
for small write I/Os.
Since you mention mail server, it is useful to know if the type of
mail server you are setting up involves a lot of synchronous writes.
The best thing you can do is to install a lot of RAM in your server to
minimize the amount of reads and writes. Lots of RAM will reduce the
amount of write activity since writes can be postponed for up to 30
seconds, and mail folders may be updated many times in the mean time.
With enough RAM installed, you will see almost all writes, with
practically no reads.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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