On 18/09/2012 11:35, GuoZhong Han wrote:
Hi Stan:
Thanks for your advice. In your last mail, you mentioned XFS
file system. According to your suggestion, I changed the file system
from raid5 (4*2T, chunksize: 128K, strip_catch_size:2048) to XFS. Then
I did a write performance test on XFS.
The test was as follows:
My program used 4 threads to do parallel writing to 30 files
with 1MB/s writing speed on each file. Each thread was bound on a
single core. The estimated total speed should be stable at 30MB/s. I
recorded the total writing speed every second in the test. Compared
with speed of ext4, when the array was going to be full, the
performance of XFS has indeed increased. The time to create the XFS
file system was much less than the cost of ext4. However, I found that
the total speed wasn’t steady. Although most of time the speed can
reach to 30M/s, it fell to only about 10MB/s in rare cases. Writing to
30 files in parallel was supposed to be easy. Why did this happen?
Two questions - what is the XFS built on? 4 x 2TB in a linear
concatenation, or something else?
Secondly, are all your files in the same directory, or in different
directories? XFS scales by using multiple threads for different
allocation groups, and putting these groups in different places on the
underlying disk or disks - but files in the same directory go in the
same allocation group. So 30 files in 30 directories will give much
more parallelism than 30 files in 1 directory.
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