On 11/26/2012 1:35 AM, Roy Sigurd Karlsbakk wrote: >> I want to know what is best chunk size to create s/w raid devices? > > That depends on the workload, file sizes etc. Correct. And greatly depends on array type. > The default will probably do fine This is not true of metadata 1.2 and parity arrays in which case the default chunk size is 512KB. That's way too large for anything but large file streaming workloads. Most workloads involve metadata and small files. This has been discussed previously in detail on this list and on the XFS list. For most workloads other than large file streaming, mirroring+striping is best, but if you must use parity RAID a small chunk size of 32/64KB yields superior IO performance due to decreased overhead during RMW. >> Also is it possible to change the chunk size for an existing array? No. You must destroy and recreate it with the new chunk size. If one creates an array with an appropriate chunk size there is no need to ever change it, UNLESS the primary workload hitting the array changes from random IO to large streaming, or the reverse. In such a case one typically builds a new server with a new array, or simply adds a new array to the existing server for the new workload. If you are redeploying the server/array, destroy and recreate with the new optimal chunk size. -- 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
