Re: Preliminary performance benchmarks.

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On Thu, Apr 12, 2012 at 5:05 PM, Leen Besselink <leen@xxxxxxxxxxxxxxxxx> wrote:
> (I've been lurking the mailinglist archive for a few months already, I think
> bcache sounds really interresting)
>
> Hello Joseph,
>
>> Carrying out some scalability tests on high I/O systems. More tests to
>> come using the Phoronix Test Suite.
>>
>> Fio summary:
>> 24 jobs
>> Direct IO
>> Randwrite test
>> Total of about 80k IOPs at 3.5k IOPS per thread.
>>
>> Test rig specs:
>> 2x Intel(R) Xeon(R) CPU X5650  @ 2.67GHz (12 physical cores, 24 logical)
>> 12x 2TB Seagate nearline-SAS in RAID6 on LSI Logic / Symbios Logic LSI
>> MegaSAS 9260
>> 2x Intel 520 SSDs 120GB in RAID0
>>
>> The 2 520s are striped with md raid as /dev/md0 whch is formatted as a
>> bcache cache device using 1M buckets and 8k hard block size
>> Backing device is the big old raid6.
>>
>> Random IO performance of the native raid0 is about 96K IOPs, backing
>> device in the realm of 1600ish.
>> However the backing device has a sequential IO performance of about 1.5GB/s.
>>
>
> So why do you put your SSDs in RAID0 ?
>
> If you are using RAID6 for your HDD you obviously care about your data, shouldn't
> you be using RAID1 or let bcache do some RAID1-like behaviour* ?
>
> Because when you use RAID0 your data will only be written to one SSD.
>
> * I think bcache had some ability to handle that sort of automatically.

That's been in the design since forever, but I haven't gotten around
to finishing it since we haven't needed it internally.

(But yes, the idea is to have multile SSDs in a cache set, with only
dirty data and metadata mirrored. Wouldn't be a _huge_ amount of work
to finish.)

>
>> Below are some quick findings using fio - showing very good
>> scalability of bcache even with very very fast SSDs.
>> *Note: The SSDs are connected via a SATA2 interface being somewhat of
>> a bottleneck.
>
> Have a nice day,
>        Leen.
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