Messages in this thread | | | From | "Oliver S." <> | Subject | AW: Benefits from computing physical IDE disk geometry? | Date | Sun, 13 Apr 2003 01:10:05 +0200 |
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> Any good SCSI drive knows the physical geometry of the disk and can > therefore optimally schedule reads and writes.
If the scheduler inside the OS can rely on the drive to have a linear mapping it is implemented as a cyclical-scan scheduler, there is only a little difference in the effectivity of the scheduling.
> Although necessary features, like read queueing, are also available > in the current SATA spec, I'm not sure most drives will implement it, > at least not very well.
AFAIK the Seagate Barracudas implement first-party-dma, which is a very lightweight implementation of command-queuing; with first-party -dma, the CPU includes the adresses of where the data for a certain request is read or written into the request-command so that when the disk responds to a command, it sends this information back to the controller. So this chip doesn't have to hold a list of outstanding requests and their scattered adresses where the data is read from or written to. Doesn't look very elegant, but that's just in line with the cheap ATA-concepts. And the only controller-chips I'm aware of supporting this features are the chips fom Silicon Image. But I think that sooner or later, all SATA-chips will support it.
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