Fron the zpool man page:
By default, the intent log is allocated from blocks within the main pool.
However, it might be possible to get better performance using separate
intent log devices such as NVRAM or a dedicated disk.
I was also contemplating the idea of a fast SSD on PCIe as a ZIL and L2ARC.
And given the fact that the SSD will not suffer from the different types and
locations of IO requests,
maybe it makes sense to go with a big SSD, and partition it for a small ZIL
partition,
and the rest for L2ARC. Anyone tried that?
Regards,
Nikolay
On Aug 29, 2012, at 2:47 AM, Andrew Young <[email protected]> wrote:
> Thanks for the great feedback Josh! The optimum size for an ssd zil device
> was still an open question for us. I'm really glad to hear that they don't
> need to be that big.
>
> What does zfs do with the zil if there is no dedicated zil device? Our
> servers consist of a small sata drive that holds the OS and a boatload of
> larger drives on a sas bus. What I'm wondering is if I simply replace the OS
> disk with an ssd will I get the same performance boost as if I added a
> dedicated ssd zil?
>
> Thanks!
> Andy
>
> On Aug 28, 2012, at 7:07 PM, Josh Paetzel <[email protected]> wrote:
>
>>>> -------- Original Message --------
>>>> Subject: Support for Fusion IO drives?
>>>> Date: Tue, 28 Aug 2012 16:46:00 -0400
>>>> From: Andy Young <[email protected]>
>>>> To: [email protected]
>>>>
>>>>
>>>> We are investigating adding SSDs as ZIL devices to boost our ZFS write
>>>> performance. I read an article a while ago about iX Systems teaming up
>>>> with
>>>> Fusion IO to integrate their hardware with FreeBSD. Does anyone know
>>>> anything about supported drivers for Fusion IO's iodrives?
>>>>
>>>> Thanks!
>>>>
>>>> Andy
>>>> _______________________________________________
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>>>> To unsubscribe, send any mail to
>>>> "[email protected]"
>>>>
>>>>
>>>>
>>>>
>>
>> I'll put on my iXsystems hat here, as well as my fast storage, ZFS and
>> Fusion-I/O hat.
>>
>> The ZFS filesystem supports dedicated ZIL devices, which can accelerate
>> certain types of write requests, notably related to fsync. The VMWare
>> NFS client issues a sync with every write, and most databases do as
>> well. In those types of environments having a fast dedicated ZIL device
>> is almost essential. In other environments the benefits of a dedicated
>> ZIL range from non-existent to substantial.
>>
>> A good dedicated ZIL device is all about latency. It doesn't need to be
>> large, in fact it will only ever handle 10 seconds of writes, so 10x
>> network bandwidth is worst case. (In most environments this means 20GB
>> is larger than needed).
>>
>> Fusion-I/O cards are far too large to be cost effective ZIL devices.
>> Even though they do rock at I/O latency, the really fast ones are also
>> fairly large, so the $/GB on them isn't so attractive. There are better
>> options for ZIL devices.
>>
>> Another consideration is the Fusion-I/O driver is fairly memory hungry,
>> which competes with memory ZFS wants to use for read caching.
>>
>> Now as an L2ARC device, that's a whole different can of worms.
>>
>> Command line used: iozone -r 4k -s 96g -i 0 -i 1 -i 2 -t 8
>> Parent sees throughput for 8 readers = 1712399.95 KB/sec
>> L2 ARC Breakdown: 197.45m
>> Hit Ratio: 98.61% 194.71m
>> L2 ARC Size: (Adaptive) 771.13 GiB
>> ARC Efficiency: 683.40m
>> Actual Hit Ratio: 71.09% 485.82m
>>
>> ~ 800GB test data, all served from cache.
>>
>> If you are considering Fusion-I/O, the FreeBSD driver is generally not
>> released to the general public by Fusion-I/O, but can be obtained from
>> various partners. (I believe iXsystems is the only FreeBSD friendly
>> fusion-i/o partner but could be wrong about that)
>>
>>
>> --
>> Thanks,
>>
>> Josh Paetzel
>>
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