[OpenIndiana-discuss] How do I swiych from IDE to AHCI mode for my SATA disks, please vet my procedure!

[Bryan N Iotti]

Just for fun, I'd take a look at the output of 'iostat -xen <time interval>', paying attention to the asvc_t column... That value probably went way down with the move from IDE to AHCI, due in part to the lighter CPU load of native SATA commands (less interrupts?) coupled with the performance benefits of native command queueing.

If I'm not wrong, if your asvc_t is higher than 10.0 you will experience a sluggish response from the disk, and the whole system if it's your rpool.

As always, please point out inaccuracies in my thought, as I'm eager to learn more but I'm quite new in performance monitoring.

Bryan
Sent from my BlackBerry® wireless device from WIND

-----Original Message-----
From: Jim Klimov <jimklimov at cos.ru>
Date: Tue, 19 Mar 2013 13:04:48 
To: <openindiana-discuss at openindiana.org>
Reply-To: Discussion list for OpenIndiana <openindiana-discuss at openindiana.org>
Subject: Re: [OpenIndiana-discuss] How do I swiych from IDE to AHCI mode for
 my SATA disks, please vet my procedure!

On 2013-03-19 12:20, Hans J. Albertsson wrote:
> Now, if somebody can explain why my old and trusty SunRay2 units
> suddenly display scrolling items much much faster.... Say like from
> impossibly slow with large bytewise block rewrites to almost like
> accelerated local displays.
>
> Just because I set the SATA mode to AHCI w/o Legacy mode...

I might guess that the IDE interrupts are more costly while SATA/SCSI
ones are more offloaded to hardware, leaving your CPUs more available
and responsive for small urgent tasks?

In fact, even for VMs it is a stated reason to prefer SATA/SCSI vHBAs
to IDE ones, except for maybe rarely used vCDROMs.

> Maybe it's just that sometimes the Byte Fairy is generous.

Yup, that's the more likely explanation :)

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