Re: OT: Re: [gentoo-user] X Freezes With Firefox on Many Post 2.6.38 Kernels

[Peter Humphrey <peter@humphrey.ukfsn.org>]

On Sunday 31 July 2011 15:17:16 Joshua Murphy wrote:

> There probably is a fair chunk of difference in maximum speed the disk
> can work at on each end (I've even seen around a 20MB/s difference on
> several 160GB drives I've dealt with), but outside of some older
> drives that've been heavily abused in their lives, I'm not sure I've
> seen a sata drive that I've used my usual drive test (MHDD on a
> Hiren's bootable USB) on register below around 60MB/s on the slow end,
> and USB2's *theoretical* limit is 480Mb/s (60MB/s) ... real-world
> implementations rarely reach, let alone top, around 40MB/s, so disk
> speed variation across the disk is an unlikely source of the slowdown.

Sounds entirely reasonable, and I wasn't really trying to blame the slowness 
on that variation - just mentioning it in passing.

> More likely, it's the fact that parted has to start from the end, and
> work its way backwards, reading, writing, and verifying in separate
> rotations of the disk with no benefit from the drive's ability to
> stream a larger block into cache, since the whole process is backwards
> compared to the streaming read most drives are optimized for.

Perhaps I'm naive here, but I should have thought an intelligent disk 
copying algorithm would be able to account for that, at least in part. Maybe 
that's why it ran the speed tests at the beginning.

> Of course, this is all off the cuff conjecture on my part, including my
> assumptions about how parted approaches the whole task... mixed with a
> bit of anecdotal evidence on my end... but, makes for amusing
> conversation and contemplation, if nothing more substantial.

Indeed.

> I will point out that the newer advanced format WD 500GB blue's I've
> worked recently with pulled a consistent 120-110MB/s speed from end to
> end... when their older 320s usually peaked at around 85 or so.

Well, I haven't run any proper tests, but watching gkrellm during an 
occasional large transfer I don't remember seeing more than half that lower 
figure. These are two Samsung Spinpoint F3 1TB disks in md-raid with LVM-2, 
and I haven't fiddled with any of their settings.

-- 
Rgds
Peter		Linux Counter 5290, 1994-04-23