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
