On Tuesday, 11 July 2006 at 16:41:24 -0700, Chris White wrote: > On Tuesday 11 July 2006 04:18 pm, Brian Dunning wrote: >> My understanding is that SCSI has a faster transfer rate, for >> transferring large files. A busy database needs really fast access, >> for making numerous fast calls all over the disk. Two different, >> unrelated things. >> >> I am more than willing to be called Wrong, slapped, and cast from a >> bridge. > > Be careful on that, databases do more work in memory than anything > else. That said, I'd be more worried about your memory capacity. > Now, if you rely mainly on swap(virtual) memory, then you might > worry more on that :).
Clearly when you're working in memory, the kind of disks you use don't have much influence. In fact, SCSI disks typically have (marginally) faster access times than ATA. They may also have higher transfer rates, but as Brian observes, this is of marginal interest. One of the things that we discuss internally from time to time is the influence of block size on database performance. On modern disks, random access to a single 4 kB block takes about 5.1 ms (5 ms seek, 0.1 ms transfer). Random access to a single 64 kB block takes about 6.6 ms (5 ms seek, 1.6 ms transfer). Clearly big blocks improve disk bandwidth; but if you only need 4 kB, the rest doesn't buy you anything. That's why we discuss rather than come to any useful conclusion. Greg -- Greg Lehey, Senior Software Engineer, Online Backup MySQL AB, http://www.mysql.com/ Echunga, South Australia Phone: +61-8-8388-8286 Mobile: +61-418-838-708 VoIP: sip:[EMAIL PROTECTED], sip:[EMAIL PROTECTED] Diary http://www.lemis.com/grog/diary.html Are you MySQL certified? http://www.mysql.com/certification/
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