On Tue, 2003-03-11 at 14:30, Kirk Strauser wrote: > At 2003-03-11T18:41:12Z, Ron Johnson <[EMAIL PROTECTED]> writes: > > > Why wouldn't you get parallel reads, especially if you do async IO? > > I guess a better example would be when two files are accessed, and each > has blocks that physically reside on the same two drives. Imagine that both > files are accessed randomly and concurrently (think multiple database > instances). In this case, it could very well happen that blocks from file1 > (f1a, f1b) and file2 (f2a, f2b) are being read simultaneously. In this > case, both drives are jumping back and forth between f1a/f2a and f1b/f2b.
2 issues: 1. Tagged command queuing should order the reads. 2. As a DBA, it seems to me that this possibility is irrelevant, since the DBMS would have sucked those blocks (and their neighbors) into it's cache after the 1st 1 or 2 db read requests. > Imagine, instead, that file1 and file2 are on a mirror. The RAID system > could converge on the situation where the first drive is "dedicated" to > file1, and the second is "dedicated" to file2. > > I don't think this is a particularly unlikely scenario. Are controllers smart in that way? -- +---------------------------------------------------------------+ | Ron Johnson, Jr. mailto:[EMAIL PROTECTED] | | Jefferson, LA USA http://members.cox.net/ron.l.johnson | | | | Spit in one hand, and wish for peace in the other. | | Guess which is more effective... | +---------------------------------------------------------------+ -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
