Re: Preliminary performance benchmarks.

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On 13 April 2012 10:05, 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.

I used RAID0 to demonstrate bcache scaling to 80k IOPs, this was not a
production machine nor a production configuration.

Yes, atleast somewhat. Bcache cache devices are structured into
cache-sets, which are groups of SSDs that form one logical cache which
you can attach multiple backing devices to.
This is different from RAID1 because only dirty data is mirrored. You
don't need redundant copies of your read cache but you care very much
that you don't lose writeback cache data.
This isn't fully fleshed out in bcache yet but all the infrastructure
is there, I am looking to doing some work on it soonish I have just
been busy with other things.
>
>> 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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Joseph.

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