Dan, Thanks for your reply. Still get two questions left. Suppose I have a MD-RAID5 array which consists of 8 disks. 1. Do we need to consider the chunk size of the RAID array when we set the value of Striped_Cache_Size? For example, if the chunk size is changed from 64k to 256k, do we need to adjust the Striped_Cache_Size accordingly? 2. The performance improvement of large size I/O packets (128k, 256k) is larger than small size I/O packets (512B, 1KB) when I change the Striped_Cache_Size. How do you explain the difference here? Liang -----Original Message----- From: dan.j.williams@xxxxxxxxx [mailto:dan.j.williams@xxxxxxxxx] On Behalf Of Dan Williams Sent: Sunday, January 21, 2007 11:07 PM To: Liang Yang Cc: linux-raid@xxxxxxxxxxxxxxx Subject: Re: What is the exacting meaning of Striped_Cache_Size? On 1/21/07, Liang Yang <multisyncfe991@xxxxxxxxxxx> wrote: > Hello, > > I have tried to increase the Striped_Cache_Size from 256 (default for my > MD-RAID5 array) to 8192, it does improve the MD-RAID5 Write performance > which varies with the size of I/O packet. > > However, I'm still not very clean the meaning and the potential performance > impact of this Striped_Cache_Size? Is the unit for this parameter Byte or > KiloByte? > > Could anyone here explain with a little bit more details? > stripe_cache_size is the number of stripes in the cache. Each stripe (strip) is composed one PAGE_SIZE block per disk. If your page size is 4k and you have 4 disks in your array then a stripe_cache_size of 256 is 4k * 4 * 256 = 4MB. Increasing this number increases the chances that a write to the array will not generate reads to satisfy the parity calculation. > Thanks, > > Liang > Regards, Dan - 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
