On Fri, 20 Feb 2009, Sitsofe Wheeler wrote:

Whoops, I didn't mean to send that previous half formed mail :) Sorry.

As mentioned in another mail there was a discussion on
http://lkml.org/lkml/2009/1/31/28 and long thread talking about the
introduction of the rotational flag here
http://lkml.org/lkml/2009/1/5/340 . Cheapo SSDs or even USB keys are not
auto detected as non-rotational devices by the kernel and after a bit of
poking about I've come up with the following udev rules for my
particular cases:

SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{model}=="ASUS-PHISON *", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{idVendor}=="0951", ATTRS{idProduct}=="1606", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{manufacturer}=="SanDisk", ATTRS{product}=="Cruzer Micro", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"

Ever since the rotational option appeared I've been trying cfq but prior
to that I was using noop or deadline. However it doesn't look like
anyone has sat down and run the numbers to see what affect the
ioscheulder/rotational flag is having on cheapo SSDs - all the
suggestions are anecdotal. Could you run some benchmarks with these
different options and report back the results?

-- 
Sitsofe | http://sucs.org/~sits/

$ grep rotational -r /usr/src/linux/
/usr/src/linux/drivers/scsi/NCR5380.c: * USLEEP_POLL should be a maximum rotational latency.
/usr/src/linux/fs/partitions/sun.c:             __be16 rspeed;     /* Disk rotational speed */
/usr/src/linux/fs/ufs/ufs_fs.h: * Compute the cylinder and rotational position of a cyl block addr.
/usr/src/linux/fs/ufs/ufs_fs.h: __fs32  fs_nrpos;               /* number of rotational positions */
/usr/src/linux/fs/ufs/ufs_fs.h:#define UFS_42POSTBLFMT          -1      /* 4.2BSD rotational table format */
/usr/src/linux/fs/ufs/ufs_fs.h:#define UFS_DYNAMICPOSTBLFMT     1       /* dynamic rotational table format */
/usr/src/linux/fs/ufs/ufs_fs.h: __s32   s_nrpos;        /* number of rotational positions */
/usr/src/linux/include/linux/blkdev.h:#define QUEUE_FLAG_NONROT      14 /* non-rotational device (SSD) */
/usr/src/linux/include/linux/genhd.h:   __u16   d_rpm;                  /* rotational speed */

# find /sys/|grep -i rotational
#

Which kernel{option} do you enable to enable support for that option in /sys?

Justin.