Date: Sun, 6 May 2001 09:43:59 +1000 From: "Jan Mikkelsen" <janm@transactionware.com> To: "Doug Russell" <drussell@saturn-tech.com>, "Matt Dillon" <dillon@earth.backplane.com> Cc: "freebsd-stable" <freebsd-stable@FreeBSD.ORG> Subject: Re: soft update should be default Message-ID: <00b601c0d5bd$42ba1340$0901a8c0@haym.transactionsite.com>
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Doug Russell <drussell@saturn-tech.com> wrote: >On Sat, 5 May 2001, Matt Dillon wrote: > >> Not only will the hard drive not be able to write the write-cached >> data to the media, but IDE hard drives will not guarentee write >> ordering either. Someone did a test a while back and found that >> under heavy disk loads an IDE drive could hold some of the dirty data >> in its cache for an indefinite period of time without writing it out. >> i.e. it would write out some of the dirty data but also hold some of it >> indefinitely, unwritten. > >Blech. IDE. Need I say more? :) >(Yes, I do have some IDE disks, but I prefer SCSI. Don't we all? :) ) >I don't have WCE on any IDE disk i can think of, but I don't normally run >it on my SCSIs, either, unless I specifically need the write speed. Good write speed is possible without using write cache by using tagged command queueing. Have you measured tagged command queueing vs. write cache for write speed on your SCSI drives? I get about the same (~23MB/sec) on an IBM DLTA-307030 Ultra ATA drive (tags/no WC vs. no tags/WC). With neither option, it is terrible, of course. The question is how much performance the write ordering constraints in the softupdates protocol removes. I have no idea, and I'm sure it would depend on all sorts of stuff. Hopefully, aggregate throughput would be high, even if individual operations were slow. Jan Mikkelsen To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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