Date: Tue, 15 Apr 2003 23:41:28 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Alain Fauconnet <alain@ait.ac.th> Cc: Jason Stone <freebsd-performance@dfmm.org> Subject: Re: tweaking FreeBSD for Squid using Message-ID: <3E9CFB18.8ECD3502@mindspring.com> References: <20030416021004.GA7867@ait.ac.th> <20030416024844.GC7867@ait.ac.th>
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Alain Fauconnet wrote: > I don't know. Seems that IDE disks evolve too fast for me nowadays. > That's also why I was writing that I'm not even sure that the old > stance "don't use IDE for servers" is still valid. > OOTH, I've had a lot of trouble with busy IDE-based (ASUS P4* m/b) > FreeBSD servers lately (hard hangs, see bug kern/44867). FWIW: IDE disks do not support disconnected writes, which is a significant performance bottleneck when you are writing to the disk; only disconnected reads are supported. What this means is that, depending on your content, you could take a big performance hit for anything you write to cache. It's a pretty common practice these days for active content to permit itself to be cached, but have a short expiration; even if that weren't the case, there's plenty of cacheable content out there (think "pretty much every image"). What's worse is that this is precisely the larger content, which is exactly what you would most want to write to disk. I guess it really depends on why you are proxy-caching the stuff in the first place. If it's because you have a lot of users behind a big pipe, then you are probably going to end up being I/O bound on the disk. I definitely agree with you that you are better off with multiple cache dirs than with RAID-0... on the other hand, it could be worth it to have multiple disks, if you are using IDE, since you get one concurrent outstanding write per IDE disk you add. To get 8 concurrent writes, you pretty much need 8 disks, and the only way to get something like that would be an IDE RAID controller. Personally, I'd just spring the extra hundred bucks for the SCSI, though, and get 128 or more concurrent writes, instead (tagged command queue depth). -- Terry
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