From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Andrew Herdman" Subject: Re: RAID1 VS RAID5 Date: Mon, 27 Oct 2003 10:52:46 -0500 Sender: linux-raid-owner@vger.kernel.org Message-ID: <00da01c39ca2$5da252e0$0180a8c0@what> References: <1067179519.1222.107.camel@cala> <200310270933.37564.dusty@strike.wu-wien.ac.at> <200310271201.10418.dusty@strike.wu-wien.ac.at> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: To: linux-raid@vger.kernel.org List-Id: linux-raid.ids My P4-2.4GHz with 3 WD80G 8MB caches does significantly better with RAID5 hdparm -tT /dev/md/3 /dev/md/3: Timing buffer-cache reads: 1844 MB in 2.00 seconds = 921.08 MB/sec Timing buffered disk reads: 166 MB in 3.00 seconds = 55.26 MB/sec md3 : active raid5 ide/host4/bus0/target0/lun0/part3[1] ide/host2/bus1/target0/lun0/part3[2] ide/host2/bus0/target0/lun0/part3[0] 143713280 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU] Linux why 2.4.22-ck2-blackbox-aph-21 #1 Wed Sep 17 09:41:14 EDT 2003 i686 GNU/Linux This kernel also has the low latency and preempt patches applied and running at 500hz. Andrew ----- Original Message ----- From: "Hermann Himmelbauer" To: "Gordon Henderson" ; Sent: Monday, October 27, 2003 6:01 AM Subject: Re: RAID1 VS RAID5 > On Monday 27 October 2003 10:19, Gordon Henderson wrote: > > On Mon, 27 Oct 2003, Hermann Himmelbauer wrote: > > > My experience is that software RAID5 is quite slow. > > > > My experiences are the opposite to yours I'm afraid - I've not found it > > any slower than a single drive and in some cases a lot faster! > > > > A lot depends on exactly what you are doing with it though, but I'm > > willing to sacrifice some speed for data integrity. > > > > Most of my systems are network servers with 100Mb Network cards fitted - > > as long as my disk systems are faster than 12.5MB/sec I'm happy. In > > practice I can stream 50MB/sec+ out of some simple RAID5 IDE systems I > > have. > > Well - I have an old Dual P-II-266 System with an onboard SCSI-Controller with > 3 Ultra SCSI-disks connected, building a RAID5. I did a simple Test with > "hdparm -tT" to provide you with numbers: > > /dev/sdb: > Timing buffer-cache reads: 128 MB in 1.46 seconds = 87.67 MB/sec > Timing buffered disk reads: 64 MB in 5.07 seconds = 12.62 MB/sec > > /dev/sdc: > Timing buffer-cache reads: 128 MB in 1.47 seconds = 87.07 MB/sec > Timing buffered disk reads: 64 MB in 4.78 seconds = 13.39 MB/sec > > /dev/sdd: > Timing buffer-cache reads: 128 MB in 1.49 seconds = 85.91 MB/sec > Timing buffered disk reads: 64 MB in 5.05 seconds = 12.67 MB/sec > > So you see, the seperate disks achieve ~ 13MB/s. My RAID5 raidtab looks like > this: > raiddev /dev/md0 > raid-level 5 > nr-raid-disks 3 > nr-spare-disks 0 > chunk-size 4 > persistent-superblock 1 > parity-algorithm left-symmetric > device /dev/sdb2 > raid-disk 0 > device /dev/sdc2 > raid-disk 1 > device /dev/sdd2 > raid-disk 2 > > And "hdparm -tT" looks like this: > > /dev/md0: > Timing buffer-cache reads: 128 MB in 1.45 seconds = 88.28 MB/sec > Timing buffered disk reads: 64 MB in 13.85 seconds = 4.62 MB/sec > > So this is ~ 1/3rd of the read performance of a single disk. And this is what > a appr. measure when copying files etc. > > My kernel version is 2.4.20 and the CPU-Load during the hdparm test is only at > ~ 30%. > > Best Regards, > Hermann > > -- > x1@aon.at > GPG key ID: 299893C7 (on keyservers) > FP: 0124 2584 8809 EF2A DBF9 4902 64B4 D16B 2998 93C7 > > - > 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 >