Gentoo Archives: gentoo-user

From: Peter Humphrey <peter@××××××××××××××.org>
To: gentoo-user@l.g.o
Subject: Re: OT: Re: [gentoo-user] X Freezes With Firefox on Many Post 2.6.38 Kernels
Date: Sun, 31 Jul 2011 15:01:10
In Reply to: Re: OT: Re: [gentoo-user] X Freezes With Firefox on Many Post 2.6.38 Kernels by Joshua Murphy
1 On Sunday 31 July 2011 15:17:16 Joshua Murphy wrote:
3 > There probably is a fair chunk of difference in maximum speed the disk
4 > can work at on each end (I've even seen around a 20MB/s difference on
5 > several 160GB drives I've dealt with), but outside of some older
6 > drives that've been heavily abused in their lives, I'm not sure I've
7 > seen a sata drive that I've used my usual drive test (MHDD on a
8 > Hiren's bootable USB) on register below around 60MB/s on the slow end,
9 > and USB2's *theoretical* limit is 480Mb/s (60MB/s) ... real-world
10 > implementations rarely reach, let alone top, around 40MB/s, so disk
11 > speed variation across the disk is an unlikely source of the slowdown.
13 Sounds entirely reasonable, and I wasn't really trying to blame the slowness
14 on that variation - just mentioning it in passing.
16 > More likely, it's the fact that parted has to start from the end, and
17 > work its way backwards, reading, writing, and verifying in separate
18 > rotations of the disk with no benefit from the drive's ability to
19 > stream a larger block into cache, since the whole process is backwards
20 > compared to the streaming read most drives are optimized for.
22 Perhaps I'm naive here, but I should have thought an intelligent disk
23 copying algorithm would be able to account for that, at least in part. Maybe
24 that's why it ran the speed tests at the beginning.
26 > Of course, this is all off the cuff conjecture on my part, including my
27 > assumptions about how parted approaches the whole task... mixed with a
28 > bit of anecdotal evidence on my end... but, makes for amusing
29 > conversation and contemplation, if nothing more substantial.
31 Indeed.
33 > I will point out that the newer advanced format WD 500GB blue's I've
34 > worked recently with pulled a consistent 120-110MB/s speed from end to
35 > end... when their older 320s usually peaked at around 85 or so.
37 Well, I haven't run any proper tests, but watching gkrellm during an
38 occasional large transfer I don't remember seeing more than half that lower
39 figure. These are two Samsung Spinpoint F3 1TB disks in md-raid with LVM-2,
40 and I haven't fiddled with any of their settings.
42 --
43 Rgds
44 Peter Linux Counter 5290, 1994-04-23