Date: Fri, 16 Sep 2011 16:08:33 +0200 From: "Svein Skogen (Listmail account)" <svein-listmail@stillbilde.net> To: freebsd-questions@freebsd.org Subject: Re: FS of choice for max random iops ( Maildir ) Message-ID: <4E735861.3040302@stillbilde.net> In-Reply-To: <20110916095745.872947fg6vym1vy8@mail.top-consulting.net> References: <20110916063153.200375qdq59crf8c@mail.top-consulting.net> <32990703-D068-4B0D-AF3A-C1E6EA0A4100@elde.net> <20110916095745.872947fg6vym1vy8@mail.top-consulting.net>
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On 16.09.2011 15:57, freebsd@top-consulting.net wrote:
> Quoting Terje Elde <terje@elde.net>:
>=20
>> On 16. sep. 2011, at 12:31, freebsd@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
>=20
> 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.
//Svein
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