On Tue, Feb 17, 2004 at 09:50:21AM -0800, Gregory Leblanc wrote: > Keld Jørn Simonsen wrote: > > >Hi > > > >I have some strange performance results on a raid0 > >I have 4 IDE disks on two controllers, the one on the > >motherboard of the duron 1 GHz mackine, the other a promise TX2 plus > >SATA + PATA controller. I run kernel 2.4.22 > > > >The disks and hdparm -t on each of them > > > >/dev/hdc1 seagate 80 GB 16 MB/s > >/dev/sda1 maxtor sata 200 GB 50 MB/s > >/dev/sdb7 maxtor 160 GB 54 MB/s > > Well, if you're lucky, these might be useful as comparative numbers > between the different drives on the same system. Just as likely not, > though, hdparm rather sucks as a benchmark. Yes, I only use them as crude benchmark measuers, but they seem indicative. > >The partitions are al about 5 GB each. > > > >If I make a raid0 device of all of them I get a thruput of 45 MB/s > >IIf I exclude the hdc1 partition, I get around 75 MB/s. > >The system is a little loaded - but that would be normal operating > >conditions. CPU is 90 % idle. I have about 100 MB free RAM. > > Let's assume that the above numbers have a basis in reality. :) If > you've got disks with widely varying speeds, then the best performance > can often be hand from setting up a linear RAID volume, rather than a > RAID0. RAID 0 is really designed to have matching disks, as it > distributes data evenly across them. With Linear, and ext2 (erm, I'm > assuming 3 as well, I haven't heard anything different), you can > sometimes get better performance with smaller writes, because ext2 > "scatters" data around the filesystem, in order to avoid fragmentation. Yes, that would be an idea. Anyway I replaced the hdc1 with hda1 on a seagate 40 GB disk, which hdparm said could do about 40 MB/s, and then - when I was lucky, I could actually get about 120 MB/s thruput on a "cat file >/dev/null", 681 MB in 5.63 secs. This on a mildly loaded production system. Not bad! Then I am beginning to hit the 1 Gbit/s limit on the PCI bus. Best regards Keld - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
