Re: Problems with speed & "Info For" [SCSI VS ATA at the hardware level]
Re: Problems with speed & "Info For" [SCSI VS ATA at the hardware level]
- Subject: Re: Problems with speed & "Info For" [SCSI VS ATA at the hardware level]
- From: email@hidden
- Date: Mon, 18 Feb 2002 05:43:55 EST
Another thought about times required for the "Info For" request just occurred
to me: driver issues and storage medium limitations. Specifically, the
specification for ATA drives indicate they are not capable of blind
transfers, nor multiple-request (stacked-request) self-optimization at the
drive, while SCSI drives are, if I understand correctly. [source: FWB Guide
to Storage, ISBN 0-9651915-1-6]
That would mean, given 500 files in the folder, each file being required to
pass information back from the drive to the originating call from the finder
would be executed as follows:
ATA - activate the ATA channel to the device, send request for file 1, wait
for response, receive response, send request for file 2, wait for response,
send request for file 3, etc... Requires 500 request-fulfill loops at the
hardware level, each one waiting for the previous one to fulfill before being
executed.
SCSI - activate the SCSI channel, send requests for files 1 - 500 (there may
be a limit to how many requests can be asked for at a time, either all at
once, or a max of at least 16 per request), release channel & wait for
responses. Drive optimizes requests based on a seek algorithm, starts
fulfilling the requests in the order that would be most efficient to
complete, returning responses as they are capable of being completed.
Requires between 1 and a max of 32 requests [500/16, for 500 files], and 500
[optimized] fulfills at the hardware level.
That could make a phenominal speed difference, even discounting dissimiliar
transfer speeds.
Just a thought
=-= Marc
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