On Monday 27 October 2003 14:40, Gordon Henderson wrote: > On Mon, 27 Oct 2003, Hermann Himmelbauer wrote: > > 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 > > It's possibly the "old Dual P-II-266" that may be slowing things down > here. I also thought this at first. But looking at the system load with e.g. "top" or a graphic CPU-monitor the CPU load is only ~ 15%. When reading from a single drive, the load is higher, something like 25%. Moreover the most CPU-hungry application is the "hdparm"-Utility. The raid5d uses only ~ 2%. > On one of my systems: (Dual Athlon 2.4 with 2 Promise PCI IDE cards and 4 > drives): > /dev/hdg6: > Timing buffer-cache reads: 128 MB in 0.48 seconds =266.67 MB/sec > Timing buffered disk reads: 64 MB in 1.49 seconds = 42.95 MB/sec > /dev/md4: > Timing buffer-cache reads: 128 MB in 0.50 seconds =256.00 MB/sec > Timing buffered disk reads: 64 MB in 0.97 seconds = 65.98 MB/sec > > On another server (Dual PIII/Xeon 700MHz with SCSI drives) > /dev/sdc6: > Timing buffer-cache reads: 128 MB in 0.59 seconds =216.95 MB/sec > Timing buffered disk reads: 64 MB in 3.39 seconds = 18.88 MB/sec > /dev/md4: > Timing buffer-cache reads: 128 MB in 0.57 seconds =224.56 MB/sec > Timing buffered disk reads: 64 MB in 0.75 seconds = 85.33 MB/sec That's interesting: both systems are 4-disk RAID5 arrays. The first gains ~50% read performance, the second gains ~ 470% (!) - probably there is caching involved. Probably hdparm is not the best tool for benchmarking RAIDs... > So my advice is that if you want speed, be prepared to spend the £££ to > get that speed (and I don't consider these servers particularly fast, but > they are fast enough for my application which is NFS & Samba serving a > small company of engineers (software/hardware) via a single 100MB/sec > Ethernet interface). Well, 5MB/s are o.k. for my server and my application - anyway it's interesting why this happens. 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
