Hi... Well, that explains a lot, thanks.
I'm not running RAID, this is just a single UDMA/33 disk. But... what about that extra bandwidth helping with transferring data from the HDD's own cache? And I have just heard mention of solid-state HDDs. What are those? Alex On 20 Jul 1998, Gary L. Hennigan wrote: > Date: 20 Jul 1998 09:06:15 -0600 > From: "Gary L. Hennigan" <[EMAIL PROTECTED]> > To: debian-user@lists.debian.org > Subject: Re: hdparm > Resent-Date: 20 Jul 1998 15:06:18 -0000 > Resent-From: debian-user@lists.debian.org > Resent-cc: recipient list not shown: ; > > Alexander <[EMAIL PROTECTED]> writes: > | Hi... > | > | Umm: > | > | /dev/hda: > | Timing buffer-cache reads: 64 MB in 1.61 seconds =39.75 MB/sec > | Timing buffered disk reads: 32 MB in 6.87 seconds = 4.66 MB/sec > | > | Buffer-cache reads? Uh... explain that to me please, this particular UDMA > | can't go past 33 MB/s. > > That's just the cache Linux reserves in your RAM. That's why it's > 39.75MB/s. The fastest single disk in existence is rated at about > 20MB/s. So the disk you give results for above is getting roughly > 4.66MB/s and you're getting about 40MB/s from the RAM cache. > > | But I do believe I heard of a UDMA/66 or something like that. I'm not > | using that here, though, so... > > Yes, I remember hearing something about that too. Plus, there's U2W > SCSI rated at 80MB/s. Again, for a single disk access the bandwidth, > whether it's 33 (UDMA), 40 (UW SCSI), 66 (UDMA/66) or 80MB/s (U2W > SCSI), is overkill. The fastest disks manufactured are currently the > 10,000RPM drives, e.g., Seagate Cheetah, and their peak performance is > 20MB/s, and that's peak, which means probably only when > reading/writing data on the outter tracks would you ever get that > rate. Of course you benefit from the extra bandwidth if you have > multiple devices on that bus, say you have UW SCSI rated at 40MB/s, > then you can run two of those Chetah's simultaneously without degraded > performance. > > My point was that if you're benchmarking a disk and you get greater > than 20MB/s you're seeing the results of caching, either in RAM or on > the disk itself. Or you have some special set up, e.g., solid state > disk (they still make these?) or a RAID. > > Gary > > > -- > Unsubscribe? mail -s unsubscribe [EMAIL PROTECTED] < /dev/null > > -- Unsubscribe? mail -s unsubscribe [EMAIL PROTECTED] < /dev/null
