On Sun, 2009-08-30 at 14:40 -0400, fred smith wrote: > On Sat, Aug 29, 2009 at 11:52:48PM -0430, Patrick O'Callaghan wrote: > > Just a quick note to call people's attention to > > http://marc-abramowitz.com/archives/2007/02/17/getting-good-performance-out-of-usb-hard-drives-in-linux/. This is a couple of years old but it worked like a charm for me. > > > > Briefly, there's a kernel parameter > > called /sys/block/sd[a,b,...]/device/max_sectors (for USB drives sda, > > sdb etc.). This specifies the maximum size of a disk I/O operation for > > USB storage devices in units of 512 bytes, the default value being 240, > > i.e. 120KB (see http://www.linux-usb.org/FAQ.html#i5). The max_sectors > > value can be changed doing "echo N > ..." as root, and can have a > > dramatic effect on write performance for USB devices such as pendrives. > > > > I tested this by writing over 2GB to a fresh VFAT filesystem on a 4GB > > Kingston Data Traveller pendrive plugged into a USB2 port with the EHCI > > driver (as indicated by dmesg). With the default setting, this took > > nearly 90 minutes including a final sync to flush the buffers. Using a > > max_sectors value of 1024 -- the highest the system would accept -- the > > time was reduced to under 16 minutes, a better than 5 times speedup. > > YMMV of course, as different brands of pendrive can have very different > > performance characteristics. > > > > Note that the value resets to the default when you unplug the drive, so > > you need to set it manually each time. I don't know if there's a way to > > do this automatically, or change the default value permanently. > > > > Sorry of everyone already knew this, but I found it so useful I just had > > to share it :-) > > No, I didn't know it! > > I was just playing with it on F12 on my eeepc 901, using a 1 gig Memorex stick. > On that hardware I cannot use any value > 1024, or I get: > > bash: echo: write error: Invalid argument. > > but copying a 640 meg file takes abouty 4:20 (4 mins, 20 sec) with the > default setting of 240 and about 40 seconds with it set to 1024. Nice > speedup. > > With an 8 gig Sandisk Cruzer I get the same error when trying to use a > value > 1024, so it's not caused by the USB stick, but by some limitation > in the system (despite what it says in the USB FAQ referenced above about > there being no kernel limit.) It turns out that the FAQ is wrong. Perhaps it's out of date. In /usr/share/doc/kernel-doc-2.6.30.5/Documentation/block/biodoc.txt we find: "The upper limit of max_sectors is 1024." poc -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list Guidelines: http://fedoraproject.org/wiki/Communicate/MailingListGuidelines
