Re: raid10: unfair disk load?
Richard Scobie wrote: Jon Nelson wrote: My own tests on identical hardware (same mobo, disks, partitions, everything) and same software, with the only difference being how mdadm is invoked (the only changes here being level and possibly layout) show that raid0 is about 15% faster on reads than the very fast raid10, f2 layout. raid10,f2 is approx. 50% of the write speed of raid0. This more or less matches my testing. Have you tested a stacked RAID 10 made up of 2 drive RAID1 arrays, striped together into a RAID0. That is not raid10, that's raid1+0. See man md. I have found this configuration to offer very good performance, at the cost of slightly more complexity. It does, raid0 can be striped over many configurations, raid[156] being most common. -- Bill Davidsen [EMAIL PROTECTED] Woe unto the statesman who makes war without a reason that will still be valid when the war is over... Otto von Bismark - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: raid10: unfair disk load?
maobo wrote: Hi,all Yes, Raid10 read balance is the shortest position time first and considering the sequential access condition. But its performance is really poor from my test than raid0. Single-stream write performance of raid0, raid1 and raid10 should be of similar level (with raid5 and raid6 things are different) -- in all 3 cases, it should be near the write speed of a single drive. The only possible problematic cases is when you've some unlucky hardware which does not permit writing into two drives in parallel - in which case raid1 and raid10 write speed should be less than to raid0 and single drive. But even ol'good IDE drives/controllers, even if two disks are on the same channel, permits parallel writes. Modern SATA and SCSI/SAS should be no problem - hopefully, modulo (theoretically) some very cheap lame controllers. I think this is the process flow raid10 influence. But RAID0 is so simple and performed very well! From this point that striping is better than mirroring! RAID10 is stipe+mirror. But for write condition it performed really bad than RAID0. Isn't it? No it's not. When the hardware (and drivers) is sane anyway. Also, speed is a very objective thing, so to say - it very much depends on the workload. /mjt - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: raid10: unfair disk load?
On 12/23/07, maobo [EMAIL PROTECTED] wrote: Hi,all Yes, I agree some of you. But in my test both using real life trace and Iometer test I found that for absolutely read requests, RAID0 is better than RAID10 (with same data disks: 3 disks in RAID0, 6 disks in RAID10). I don't know why this happen. I read the code of RAID10 and RAID0 carefully and experiment with printk to track the process flow. The only conclusion I report is the complexity of RAID10 to process the read request. While for RAID0 it is so simple that it does the read more effectively. How do you think about this of absolutely read requests? Thank you very much! My own tests on identical hardware (same mobo, disks, partitions, everything) and same software, with the only difference being how mdadm is invoked (the only changes here being level and possibly layout) show that raid0 is about 15% faster on reads than the very fast raid10, f2 layout. raid10,f2 is approx. 50% of the write speed of raid0. Does this make sense? -- Jon - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: raid10: unfair disk load?
Jon Nelson wrote: My own tests on identical hardware (same mobo, disks, partitions, everything) and same software, with the only difference being how mdadm is invoked (the only changes here being level and possibly layout) show that raid0 is about 15% faster on reads than the very fast raid10, f2 layout. raid10,f2 is approx. 50% of the write speed of raid0. Have you tested a stacked RAID 10 made up of 2 drive RAID1 arrays, striped together into a RAID0. I have found this configuration to offer very good performance, at the cost of slightly more complexity. Regards, Richard - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: raid10: unfair disk load?
Michael Tokarev said: (by the date of Fri, 21 Dec 2007 23:56:09 +0300) Janek Kozicki wrote: what's your kernel version? I recall that recently there have been some works regarding load balancing. It was in my original email: The kernel is 2.6.23 Strange I missed the new raid10 development you mentioned (I follow linux-raid quite closely). What change(s) you're referring to? oh sorry it was a patch for raid1, not raid10: http://www.spinics.net/lists/raid/msg17708.html I'm wondering if it could be adapted for raid10 ... Konstantin Sharlaimov said: (by the date of Sat, 03 Nov 2007 20:08:42 +1000) This patch adds RAID1 read balancing to device mapper. A read operation that is close (in terms of sectors) to a previous read or write goes to the same mirror. snip -- Janek Kozicki | - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: raid10: unfair disk load?
On 12/22/07, Janek Kozicki [EMAIL PROTECTED] wrote: Michael Tokarev said: (by the date of Fri, 21 Dec 2007 23:56:09 +0300) Janek Kozicki wrote: what's your kernel version? I recall that recently there have been some works regarding load balancing. It was in my original email: The kernel is 2.6.23 Strange I missed the new raid10 development you mentioned (I follow linux-raid quite closely). What change(s) you're referring to? oh sorry it was a patch for raid1, not raid10: http://www.spinics.net/lists/raid/msg17708.html I'm wondering if it could be adapted for raid10 ... Konstantin Sharlaimov said: (by the date of Sat, 03 Nov 2007 20:08:42 +1000) This patch adds RAID1 read balancing to device mapper. A read operation that is close (in terms of sectors) to a previous read or write goes to the same mirror. Looking at the source for raid10 it already looks like it does some read balancing. For raid10 f2 on a 3 drive raid I've found really impressive performance numbers - as good as raid0. Write speeds are a bit lower but rather better than raid5 on the same devices. -- Jon - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: raid10: unfair disk load?
Michael Tokarev wrote: I just noticed that with Linux software RAID10, disk usage isn't equal at all, that is, most reads are done from the first part of mirror(s) only. Attached (disk-hour.png) is a little graph demonstrating this (please don't blame me for poor choice of colors and the like - this stuff is in works right now, it's a first rrd graph I produced :). There's a 14-drive RAID10 array and 2 more drives. In the graph it's clearly visible that there are 3 kinds of load for drives, because graphs for individual drives are stacked on each other forming 3 sets. One set (the 2 remaining drives) isn't interesting, but the 2 main ones (with many individual lines) are interesting. Ok, looks like vger.kernel.org dislikes png attachments. I wont represent graphs as ascii-art, and it's really not necessary -- see below. The 7 drives with higher utilization receives almost all reads - the second half of the array only gets reads sometimes. And all 14 drives - obviously - receives all writes. So the picture (modulo that sometimes above which is too small to take into account) is like - writes are going to all drives, while reads are done from the first half of each pair only. Also attached are two graphs for individual drives, one is from first half of the array (diskrq-sdb-hour.png), which receives almost all reads (other disks looks pretty much the same), and from the second half (diskrq-sdl-hour.png), which receives very few reads. The graphs shows number of disk transactions per second, separately for reads and writes. Here's a typical line from iostat -x: Dev: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util sdb0,32 0,03 22,16 5,84 2054,79 163,7479,21 0,20 7,29 4,33 12,12 sdk0,38 0,03 6,28 5,84 716,61 163,7472,66 0,15 12,29 5,55 6,72 where sdb and sdk are two halfs of the same raid1 part of a raid10 array - i.e., the content of the two are identical. As shown, write requests are the same for the two, but read requests mostly goes to sdb (the first half), and very little to sdk (the second half). Should raid10 balance reads too, maybe in a way similar to what raid1 does? The kernel is 2.6.23 but very similar behavior is shown by earlier kernels as well. Raid10 stripe size is 256Mb, but again it doesn't really matter other sizes behave the same here. The amount of data is quite large and it is laid out and accessed pretty much randomly (it's a database server), so in theory, even with some optimizations like raid1 does (route request to a drive with nearest head position), the read request distribution should be basically the same. Thanks! /mjt - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: raid10: unfair disk load?
Janek Kozicki wrote: Michael Tokarev said: (by the date of Fri, 21 Dec 2007 14:53:38 +0300) I just noticed that with Linux software RAID10, disk usage isn't equal at all, that is, most reads are done from the first part of mirror(s) only. what's your kernel version? I recall that recently there have been some works regarding load balancing. It was in my original email: The kernel is 2.6.23 but very similar behavior is shown by earlier kernels as well. Raid10 stripe size is 256Mb, but again it doesn't really matter other sizes behave the same here. Strange I missed the new raid10 development you mentioned (I follow linux-raid quite closely). Lemme see... no, nothing relevant in 2.6.24-rc5 (compared with 2.6.23), at least git doesn't show anything interesting. What change(s) you're referring to? Thanks. /mjt - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
