FS of choice for max random iops ( Maildir )

Svein Skogen (Listmail account) svein-listmail at stillbilde.net
Fri Sep 16 14:27:23 UTC 2011

On 16.09.2011 15:57, freebsd at top-consulting.net wrote:
> Quoting Terje Elde <terje at elde.net>:
>> On 16. sep. 2011, at 12:31, freebsd at top-consulting.net wrote:
>>> Right now I defined an entire array of 8TB ( all 16 disks ) separated
>>> in two pieces. 50 GB for FreeBSD to boot and the rest available to
>>> configure as storage.
>> ZFS will want to write to it's ZIL (zfs intent log) before writing to
>> the final location of the data. Even if you're not waiting for the
>> ZIL-write to disk (because of the controller ram), those writes will
>> probably make it through to disk. That gives you twice as many writes
>> to disk, and a lot more seek.
>> If you want to take zfs for a proper spin, I'd like to sugget adding
>> two small SSDs to the setup, mirrored by zfs. You can use those both
>> for the ZIL, and also as cache, for the array. That's a fairly small
>> investment these days, and I would be surprised if it didn't
>> significantly improve performance, both for your benchmark, and real
>> load.
>> Note: you might be in trouble if you loose your ZIL, thus the doubling
>> up. I *think* you can SSD a cache without risking dataloss, but don't
>> take my word for it.
>> Terje
> I know it's usually a big no-no but since I have the battery backed-up
> write cache from the raid card, can't I just disable the ZIL entirely ?

No. However, you could allow the ZIL to be written to a logical disk
with the battery-backed cache.


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