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SubjectRe: File system performance, hardware performance, ext3, 3ware RA ID1, etc.


Daniel Blueman wrote:
> Tim,
>
> Do you get the same numbers (but slightly higher, as this is will measure
> from a smaller portion of outer zones) with:
>
> # hdparm -t /dev/sda
>
> ?

I ran this test. This is a read test. What I did below was a write test.

Additionally, I ran this test:
time dd if=/dev/sda of=/dev/null bs=1024k count=1024

From that, I got 47 megs/sec. From 'hdparm -t /dev/sda', I got a
slightly lower number.

So, for reads, I'm getting good performance. 47 megs/sec at the
outer-most tracks is a bit lower than the 50+ that reviewers report, but
it's not bad.

However, I don't get anywhere near the 40+ megs/sec the reviewers say
the drive gets for writes. That model as a single drive in my wife's
computer gets about 39 megs/sec, which is great. But behind the 3ware,
the drive gets only 13 megs/sec. (iozone reports about 15 megs/sec, but
that's influenced by caching in RAM, and iozone is writing to a file on
tracks further out, I think.)

>
>
>>Adam Radford wrote:
>>
>>>Perhaps you are issuing non purely sequential IO. The card firmware
>>
>>does
>>
>>>some
>>>reodering, but at some point it will cause performance degradation. Can
>>
>>you
>>
>>>try
>>>kernel 2.6 w/xfs?
>>
>>Not any time soon, but as I mentioned earlier, I measured 13.9 megs/sec
>>when I ran this command:
>>
>> time dd if=/dev/zero of=/dev/sda2 bs=1024k count=1024
>>
>>No file system was involved; I was simply writing zeros to the block
>>device (swap partition with swap off). It took 73.522 seconds to do the
>>above operation. Also, I was running in single-user mode while doing
>>the test.
>>
>>
>>>Also, in my experience, the 'raw io' interface doesn't issue any
>>>asynchronous IO. The
>>>card _definately_ needs asynchronous IO posted to it or you will not get
>>>good results
>>>because you won't get all the drives busy.
>>
>>With RAID1, both drives will be written with the same data. There is no
>>need to be asynchronous, since it's all completely linear and sequential
>>with large data blocks.
>
>

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