Right now we use no partitions so I MD the full disk. Since my avrgq-sz is 8.0 What should I make my Chunk Size how do I look into this more? Over the holidays I did a Chunk Size of 32000 in f2 for testing but that did not seem to work very well. 512 and 1024 Chunk size is what I had before. No matter the PE size and Chunk size my avgrq-sz is 8. My real problem is just to even test one setup is about a week of copying data and building the array. That's why I am trying to get anything to help me make a better guess to how to set this all up right. How do I check if I am seeking more than expected? On Mon, Dec 21, 2009 at 4:56 AM, Goswin von Brederlow <goswin-v-b@xxxxxx> wrote: > Chris <cmtimegn@xxxxxxxxx> writes: > >> I have a pair of servers serving 10MB-100MB files. Each server has >> 12x 7200 SaS 750GB Drives. When I look at iostat I see the avgrq-sz >> is 8.0 always. I think this has to do with the fact my LVM PE Size is >> 4096 with JFS on top of that. Best I can tell the fact I have so >> many rrqm/s is not great and the reason I have that many is because my >> avgrq-sz is 8.0. I have been trying to grasp how I should come up >> with the best chunk and PE for more performance. >> >> Switch from n2 to f2 raid10? >> How do I calculate where I need to go from here with Chunk Size and PE size? > > 2 far copies means each disk is split into 2 partitions, lets call > them sda1/2, sdb1/2, ... Then sda1, sdb2 form a raid1 (md1) and sdb1, > sdc2 form a second raid1 (md2), ..... Last md1, md2, ... are combined > as raid0. That all is done internaly and more flexible. The above is > just so you can visualize the layout. Writes will always go to sdX1 > and sd(X+1)2. Reads should always go to sdX1, which is usualy the > faster part on rotating disks. > > You need to optimize the raid0 part and, probably way more important, > the alignment of your data access. If everything is aligned nicely > each request should be fully serviced by a single disk given your > small request size. And the seeks should be evenly spread out between > the disks with each disk seeking every 12 reads or twice every 6 > writes (or less). Check if you are seeking more than is expected. > > Also, on a lower level, make sure your raid does not start on a > partition starting at sector 63 (which is still the default in many > partitioning progs). That easily results in bad alignment causing 4k > chunks to land on 2 sectors. But you need to test that with your > specific drive to see if it really is a problem. > > MfG > Goswin > > -- 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
