I'm in the process of evaluating various storage options for a large array (12TB) I'm creating. First. I will preface all of this by saying that I understand the note in the kernel docs about comparing file systems under various workloads, and I acknowledge that my exact methodology isn't perfect. But it works for what I'm doing. :) This array will be used for storage of large media files (up to 20-30GB per file). I'm testing using iozone with various file sizes ranging from 4GB to 32GB. I'm pretty much settled on a RAID50 (128kb stripe size) running ext4 on top of LVM (for snapshots, future expansion, etc.). I'm running kernel 2.6.33.2, e2fsprogs 1.41.11 and util-linux-ng 2.16. The file system in question was created with the following options: mkfs -t ext4 -T large -i 524288 -b 4096 -I 256 -E stride=32,stripe-width=192 /dev/vg/lv Currently, I'm testing the effect of various mount options on an ext4 file system and my results are not what I would have expected based on the docs I have read. I wanted to bounce some of them off the list to find out if I'm completely missing something, or if my expectations were off. I'll start with the craziest one: noatime. Everything I have read says that the noatime option should increase both read and write performance. My results are finding that write speeds are comparable with or without this option, but read speeds are significantly faster *without* the noatime option. For example, a 16GB file reads about 210MB/s with noatime but reads closer to 250MB/s without the noatime option. Next is the write barrier. I'm an in a fully battery-backed environment, so I'm not worried about disabling it. From my testing, setting barrier=0 will improve write performance on large files (>10GB), but hurts performance on smaller files (<10GB). Read performance is effected similarly. Is this to be expected with files of this size? Next is the data option. I am seeing a significant increase in read performance when using data=ordered vs data=writeback. Reading is as much as 20% faster when using data=ordered. The difference in write performance is almost none with this option. Finally is the commit option. I did my testing mounting with commit=5 and commit=90. While my read performance increased with commit=90, my write performance improved by as much as 30% or more with commit=5. As I said, I'm looking for some help interpreting these results more than anything. Any insight into these results that can be provided would be appreciated. Steve -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
