On 3/28/07, Jeff Garzik <jeff@xxxxxxxxxx> wrote:
[...] NCQ provides for a more asynchronous flow. It helps greatly with reads (of which most are, by nature, synchronous at the app level) from multiple threads or apps. It helps with writes, even with write cache on, by allowing multiple commands to be submitted and/or retired at the same time.
Since people are looking under this rock, more black/not-whitelist fodder: Seagate ST3500641 (500G NL35.2 SATA) with firmware revisions earlier than 3.AEQ and ST3750640 (750G Barracuda ES SATA) with firmware ealier than 3.AEE exhibit pathological NCQ write behaviour at queue depths <= 2 when write cache is disabled. Writes will take 3 seconds to complete. That's not a typo, I really do mean 0.3 IOPS. As long as you can keep the write queue depth above 2, you'll be OK. For the record, I'm not slamming SATA or NCQ, just pointing out something to be aware of. -- Andy - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
