Stan, ok, I see. However, are there utilities out there which help one to analyze how applications on a server use the file-system over the time and help to make an educated decision regarding the chunk size? regards, Martin On Fri, Mar 7, 2014 at 11:58 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote: > On 3/6/2014 8:06 PM, Martin T wrote: >> Am I correct that optimal chunk size is usually the size of the >> average file read/written to disk divided by number of block devices >> in RAID array storing the data? For example if the average file size >> is 1024KiB and I have four disks in RAID1, then I should choose the >> chunk size around 256KiB to get the optimal read performance? Or if I >> have two drives in RAID0, then I should choose the chunk size 512KiB >> instead? Or are there better methods/benchmarks to determine the >> optimal chunk size for software-RAID? > > You're asking the wrong question. Storage architecture design always > begins with the workload. The correct question is: > > My workload (application mix) performs *most* IO in manner X, where X is > > 1. large streaming write/read > 2. small file write/read > 3. metadata heavy > > I have Y number of disk drives. I plan to use XFS/EXT4/etc filesystem. > What RAID level and chunk size are optimal for my workload, and how do > I properly tune my filesystem to my workload and storage stack? > >> Last but not least, is there a >> good utility which could help one to measure the average I/O >> read/write size? > > In flight IO size has no correlation to stripe and chunk size. What you > need to know is how your application(s) write to the filesystem and how > your filesystem issues write IOs. You should already know that the > former, and it's easy to determine the latter. > > -- > Stan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
