----- Original Message ----- From: "Raz Ben-Jehuda(caro)" <raziebe@xxxxxxxxx> To: "JaniD++" <djani22@xxxxxxxxxxxxx> Cc: "Linux RAID Mailing List" <linux-raid@xxxxxxxxxxxxxxx> Sent: Tuesday, January 10, 2006 12:25 AM Subject: Re: raid5 read performance > 1. it is not good to use so many disks in one raid. this means that in > degraded mode > 10 disks would be needed to reconstruct one slice of data. > 2. i did not understand what is raid purpose. Yes, i know that. In my system, this was the best choise. I have 4 disk node inside 4x12 Maxtor 200GB (exactly 10xIDE+2xSATA). The disk nodes sevres nbd. The concentrator joins the nodes with sw-raid0 The system is a generally free web storage. > 3. 10 MB/s is very slow. what sort of disks do u have ? 4x(2xSATA+10xIDE) Maxtor 200GB The system sometimes have 500-800-1000 downloaders at same time. In this load, the per node traffic is only 10MB/s. (~100Mbit/s) First i think the sync/async IO problem. At this time i think the bottleneck on the nodes is the PCI-32 with 8 HDD. :( > 4. what is the raid stripe size ? Currently all raid layers have 32KB chunks. Cheers, Janos > > On 1/4/06, JaniD++ <djani22@xxxxxxxxxxxxx> wrote: > > > > ----- Original Message ----- > > From: "Raz Ben-Jehuda(caro)" <raziebe@xxxxxxxxx> > > To: "JaniD++" <djani22@xxxxxxxxxxxxx> > > Cc: "Linux RAID Mailing List" <linux-raid@xxxxxxxxxxxxxxx> > > Sent: Wednesday, January 04, 2006 2:49 PM > > Subject: Re: raid5 read performance > > > > > > > 1. do you want the code ? > > > > Yes. > > If it is difficult to set. > > I use 4 big raid5 array (4 disk node), and the performace is not too good. > > My standalone disk can do ~50MB/s, but 11 disk in one raid array does only > > ~150Mbit/s. > > (With linear read using dd) > > At this time i think this is my systems pci-bus bottleneck. > > But on normal use, and random seeks, i am happy, if one disk-node can do > > 10MB/s ! :-( > > > > Thats why i am guessing this... > > > > > 2. I managed to gain linear perfromance with raid5. > > > it seems that both raid 5 and raid 0 are caching read a head buffers. > > > raid 5 cached small amount of read a head while raid0 did not. > > > > Aham. > > But... > > I dont understand... > > You wrote that, the RAID5 is slower than RAID0. > > The read a head buffering/caching is bad for performance? > > > > Cheers, > > Janos > > > > > > > > > > > > > On 1/4/06, JaniD++ <djani22@xxxxxxxxxxxxx> wrote: > > > > > > > > ----- Original Message ----- > > > > From: "Raz Ben-Jehuda(caro)" <raziebe@xxxxxxxxx> > > > > To: "Mark Hahn" <hahn@xxxxxxxxxxxxxxxxxxx> > > > > Cc: "Linux RAID Mailing List" <linux-raid@xxxxxxxxxxxxxxx> > > > > Sent: Wednesday, January 04, 2006 9:14 AM > > > > Subject: Re: raid5 read performance > > > > > > > > > > > > > I guess i was not clear enough. > > > > > > > > > > i am using raid5 over 3 maxtor disks. the chunk size is 1MB. > > > > > i mesured the io coming from one disk alone when I READ > > > > > from it with 1MB buffers , and i know that it is ~32MB/s. > > > > > > > > > > I created raid0 over two disks and my throughput grown to > > > > > 64 MB/s. > > > > > > > > > > Doing the same thing with raid5 ended in 32 MB/s. > > > > > > > > > > I am using async io since i do not want to wait for several disks > > > > > when i send an IO. By sending a buffer which is striped aligned > > > > > i am supposed to have one to one relation between a disk and an > > > > > io. > > > > > > > > > > iostat show that all of the three disks work but not fully. > > > > > > > > Hello, > > > > > > > > How do you set sync/async io? > > > > Please, let me know! :-) > > > > > > > > Thanks, > > > > Janos > > > > > > > > > > > > > > > > > > > > > -- > > > Raz > > > > > > > -- > Raz > - > 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 - 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
