Tagged Command Queuing or Larger Cache ?

[popo]

Howdy Crew,

I am about to buy a new hard disk for my FreeBSD work station.
Since FreeBSD's ATA drivers implement Tagged Command Queuing and IBM make
the only ATA disks that implement tagged command queuing ( ie since the 60GXP family ),
an IBM 40GB 120GXP "looks like" the best solution.

However, my question is:

Do the benifits from a having a larger disk cache such as the "WD 40GB 7200RPM w/8MB Cache"
has, outweigh the benefits of Tagged Command Queuing ?

Thanks

- aW

 

[Peter]

Tagged queuing, when paired with asynchronous, target initiated command completion (Disconnect/Reselect if we stay with SCSI nomenclature here), drastically improves performance in true multitasking situations, and frees up channel bandwidth, which is relevant if you have multiple drives on one cable.

How well that all works on ATA is another story. In theory, the drive is free to rearrange its answers to the host's pending requests in an order that lets it retrieve/write the data the fastest, minimizing the number of rotations, cylinder and head movements across all pending requests, rather than processing them in the order in which they came in.