On 29.10.2013 18:10, K T wrote: > Hi, > > I have a 1 TB SATA disk(WD1003FBYX) with XFS. In my tests, I preallocate a > bunch of 10GB files and write data to the files one at a time. I have > observed that the default mkfs setting(4 AGs) gives very low throughput. > When I reformat the disk with a agsize of 256mb(agcount=3726), I see better > throughput. I thought with a bigger agsize, the files will be made of fewer > extents and hence perform better(due to lesser entries in the extent map > getting updated). But, according to my tests, the opposite seems to be > true. Can you please explain why this the case? Am I missing something? > > My test parameters: > > mkfs.xfs -f /dev/sdbf1 > mount -o inode64 /dev/sdbf1 /mnt/test > fallocate -l 10G fname > dd if=/dev/zero of=fname bs=2M count=64 oflag=direct,sync conv=notrunc seek=0 I get the same bad performance with your dd statement. fallocate -l 10G fname time dd if=/dev/zero of=fname bs=2M count=64 oflag=direct,sync conv=notrunc seek=0 64+0 records in 64+0 records out 134217728 bytes (134 MB) copied, 4,24088 s, 31,6 MB/s After pondering the really hard to read dd-man-page. Sync is for 'synchronized' I/O. aka REALLY BAD PERFORMANCE. And i assume you don't really that. I think what you meant is fsync. (a.k.a. File (and Metadata) has hit stable-storage before dd exits). That is: conv=fsync So: time dd if=/dev/zero of=fname bs=2M count=64 oflag=direct conv=notrunc,fsync seek=0 64+0 records in 64+0 records out 134217728 bytes (134 MB) copied, 1,44088 s, 93,2 MB/s That gets much better performance, and in my case it can't get any better because the HDD (and encryption) just can't go any faster. -- Matthias _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
