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Hale, Read cache and read look ahead are decidedly different concepts. Read cache tries to assess the probability that a previously read set of data will be read again in the near future, and therefore attempts to retain in "cache" data that seems to have a high probability of being accessed again based on a locality of reference. Read look ahead is used when data access is sequential, and attepts to pre-buffer data that, because of the sequential nature of the data access, is likely to be requested in the near future (actually, likely in the very next request). The difference is that the read look ahead data hasn't necessarily been read recently, and, in fact, may never have been previously read since it was last written (could be days, weeks, months, or even years since it was last accessed). Both functions consume buffer space in the drive, but the similarity ends there. Bob -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Hale Landis Sent: Wednesday, June 29, 2005 9:32 AM To: [email protected] Subject: Re: [t13] Read Look Ahead This message is from the T13 list server. Curtis Stevens wrote: > This message is from the T13 list server. > Hale > I have to disagree with you. I do not have any recollection of read > ahead controlling read cache. To the best of my knowledge, this disables > look ahead in WD drives but has no effect on read cache. Quite frankly I > was shocked to hear that someone was actually interpreting the function as a > cache disable. No ATA rev has even hinted that this was a cache disable... So both you and Mark are saying there is no documented way to disable read caching in an ATA drive? It is only possible to disable the "read look ahead" part of some more complex "read caching" algorithm? Hale -- ++ Hale Landis ++ www.ata-atapi.com ++
