RAID-3? (was: cvs commit: src MAINTAINERS)
Greg 'groggy' Lehey
grog at FreeBSD.org
Sat Aug 21 01:28:46 PDT 2004
[Removing cvs-src and cvs-all]
On Friday, 20 August 2004 at 21:35:47 +0200, Pawel Jakub Dawidek wrote:
> On Thu, Aug 19, 2004 at 12:13:59PM +0930, Greg 'groggy' Lehey wrote:
> +> On Tuesday, 17 August 2004 at 15:16:12 +0200, Pawel Jakub Dawidek wrote:
> +> > On Tue, Aug 17, 2004 at 10:10:20PM +0930, Greg 'groggy' Lehey wrote:
> +> > +> On the contrary. RAID-3 requires byte-level striping, which is
> +> > +> ridiculous on the hardware that FreeBSD supports.
> [...]
> +> > Want to compare performance with vinum's RAID5?:)
> +>
> +> Feel free. But do it with more than a single process accessing the
> +> disks.
>
> Tests were done using this HW:
>
> da0 at iir0 bus 2 target 0 lun 0
> da0: <ICP Host Drive #00 > Fixed Direct Access SCSI-2 device
> da0: Tagged Queueing Enabled
> da0: 8675MB (17767890 512 byte sectors: 255H 63S/T 1106C)
> da1 at iir0 bus 2 target 1 lun 0
> da1: <ICP Host Drive #01 > Fixed Direct Access SCSI-2 device
> da1: Tagged Queueing Enabled
> da1: 8675MB (17767890 512 byte sectors: 255H 63S/T 1106C)
> da2 at iir0 bus 2 target 2 lun 0
> da2: <ICP Host Drive #02 > Fixed Direct Access SCSI-2 device
> da2: Tagged Queueing Enabled
> da2: 8675MB (17767890 512 byte sectors: 255H 63S/T 1106C)
So these are two disks + parity, right? That's not exactly a typical
setup.
> Test has been done for 10000 random requests (offset, size and operation
> type was random).
>
> RAID3:
> Number of Bytes per Requests per
> Operations processes second second
> ----------------------------------------------------------------------
> READ 3 6329500 95
> READ 15 8981047 135
> READ 100 10719314 161
> WRITE 3 5073263 76
> WRITE 15 7467387 112
> WRITE 100 8631136 129
> READ/WRITE 3 6041795 90
> READ/WRITE 15 8104847 121
> READ/WRITE 100 9494250 142
>
> RAID5:
What was the RAID-5 stripe size?
> Number of Bytes per Requests per
> Operations processes second second
> ----------------------------------------------------------------------
> READ 3 6041795 90
> READ 15 14768833 222
> READ 100 19546985 294
> WRITE 3 3479568 52
> WRITE 15 5403231 81
> WRITE 100 6211191 93
> READ/WRITE 3 4521071 68
> READ/WRITE 15 7911875 119
> READ/WRITE 100 9360528 140
>
> As you can see RAID5 is only faster in READ tests for 15 and 100 processes
> working in parallel. As I can see, RAID3 is faster in all the rest tests.
I don't really see enough to convince me either way. If you use small
RAID-5 stripes, then yes, it's possible to get better performance from
RAID-3. I'd also suggest that your figures would look very different
with five or nine disks. It would also be interested to see the
results of rawio on these configurations, and also the relative
performance of a single disk.
> Of course you are welcome to try by yourself.
Yes, of course, but I don't have time
> Anyway, if I can ask for something. Think twice before calling
> something ridiculous without understanding.
I'm sorry if I upset you, but I'm still by no means convinced of the
usefulness of RAID-3.
Greg
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