Messages in this thread |  | | Date | Tue, 26 Dec 2000 00:29:44 +0100 | From | Felix von Leitner <> | Subject | Abysmal RAID 0 performance on 2.4.0-test10 for IDE? |
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Hi,
I bought 4 ATA-100 Maxtor drives and put them on a Promise Ultra100 controller to make a single striping RAID of them to increase throughput.
I wrote a small test program that simply reads stdin linearly and displays the throughput. The block size is 100k. This is the result:
# cat /etc/raidtab raiddev /dev/md/0 raid-level 0 nr-raid-disks 4 persistent-superblock 1 chunk-size 32
device /dev/ide/host2/bus0/target0/lun0/part1 raid-disk 0 device /dev/ide/host2/bus0/target1/lun0/part1 raid-disk 2
device /dev/ide/host2/bus1/target0/lun0/part1 raid-disk 1 device /dev/ide/host2/bus1/target1/lun0/part1 raid-disk 3
Here are the results of my test program on the disk devices: # rb < /dev/ide/host2/bus0/target0/lun0/part1 27.8 meg/sec # rb < /dev/ide/host2/bus0/target0/lun0/part1 26.8 meg/sec
the other two disks have approximately the same numbers.
Here is the result of my test program on the strip set: # rb < /dev/md/0 30.3 meg/sec #
While this is faster than linear mode, I would have expected much better performance. These are the boot messages of the Promise adapter:
PDC20267: IDE controller on PCI bus 00 dev 60 PDC20267: chipset revision 2 PDC20267: not 100% native mode: will probe irqs later PDC20267: (U)DMA Burst Bit ENABLED Primary PCI Mode Secondary PCI Mode. ide2: BM-DMA at 0xec00-0xec07, BIOS settings: hde:pio, hdf:pio ide3: BM-DMA at 0xec08-0xec0f, BIOS settings: hdg:pio, hdh:pio ide2 at 0xdc00-0xdc07,0xe002 on irq 10 ide3 at 0xe400-0xe407,0xe802 on irq 10 hde: 160086528 sectors (81964 MB) w/2048KiB Cache, CHS=158816/16/63, UDMA(100) hdf: 160086528 sectors (81964 MB) w/2048KiB Cache, CHS=158816/16/63, UDMA(100) hdg: 160086528 sectors (81964 MB) w/2048KiB Cache, CHS=158816/16/63, UDMA(100) hdh: 160086528 sectors (81964 MB) w/2048KiB Cache, CHS=158816/16/63, UDMA(100)
I tuned the devices with hdparm -c 1 -a 32 -m 16 -p -u 1, for what it's worth (did not increase throughput but appeared to lessen the CPU usage).
To verify that this is not an issue of the Promise controller, I started two instances of my test tool at the same time, one working on hde, the other on hdg (the two channels). Both yielded approximately 25 meg/sec, so it does not appear to be a hardware or driver issue. Is the RAID code really this slow? Any ideas what I can do?
I am using the user space tools from raidtools-19990421-0.90.tar.bz2, but that should not have any influence, right?
I heard that there is a new, faster RAID code somewhere, but it only claimed to be faster on RAID level 5, not on striping.
Any tuning advice?
By the way: I noticed another thing: one of the Maxtor hard disks was broken. It caused the whole box to freeze solid (no numlock, no console switches, no sysrq). That to me severely limits the usefulness of IDE RAID. While SCSI problems cause trouble, too, I have never seen one cause a complete freeze. How am I supposed to hot-swap the disks? I am using VESA framebuffer, so maybe there was a panic and it simply did not appear on my screen (or in the logs).
Hope to hear from you soon (the RAID is needed on Dec 27). Should I use LVM instead of the MD code?
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