Re: standard performance (write speed 20Mb/s)

[John Robinson <john.robinson@anonymous.org.uk>]

On 17/07/2011 13:22, Iustin Pop wrote:
> On Sun, Jul 17, 2011 at 01:11:19PM +0100, John Robinson wrote:
[...]
>> # dd if=/dev/zero of=test bs=4096 count=262144
>> 262144+0 records in
>> 262144+0 records out
>> 1073741824 bytes (1.1 GB) copied, 2.5253 seconds, 425 MB/s
>>
>> And there's a badblocks running on another drive also on the ICH10.
>>
>> Having said that, I think mine's wrong too, I don't think my array
>> can really manage that much throughput. We should both be using more
>> realistic benchmarking tools like bonnie++:
>
> Or simply pass the correct flags to dd — like oflag=direct, which will
> make it do non-buffered writes.

That's still not realistic:

# dd if=/dev/zero of=test oflag=direct bs=4096 count=262144
262144+0 records in
262144+0 records out
1073741824 bytes (1.1 GB) copied, 117.434 seconds, 9.1 MB/s

Because this time we're doing a read-modify-write for every 4K block, or 
at least a write for every 4K block. I can fix it up again to work in 
stripe size amounts:

# dd if=/dev/zero of=test oflag=direct bs=1572864 count=683
683+0 records in
683+0 records out
1074266112 bytes (1.1 GB) copied, 18.3198 seconds, 58.6 MB/s

But it's still not realistic because real I/O does use buffers and 
doesn't work in magic sizes, so we should be using a more realistic 
benchmarking tool like bonnie++.

Cheers,

John.

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