On Sun, Feb 22, 2009 at 9:33 AM, Colin Watson <[email protected]> wrote: > On Sun, Feb 22, 2009 at 01:40:16AM +0100, Jim Meyering wrote: >> Daniel J Blueman wrote: >> > I've checked into this, and since libparted sees the SATA block device >> > as SCSI, it doesn't perform the expected ATA 'identify' command to >> > fill out the 512 bytes of device info, of which (short) word 217 is >> > device RPM, defined to be 1 on newer compliant SSDs. The kernel uses >> > this word to detect if a device is an SSD or not, so I suggest we use >> > the same. >> > >> > Anyone think of objections to calling the ATA identify ioctl to fill >> > out the structure, then storing this flat for later use in constraint >> > checking? If the SCSI device supports it also, fine, else nothing >> > lost. >> > >> > For now, a 1MB starting offset for an SSD seems safest, and is what MS >> > Windows 7 and Server 2008 use, thus a number of vendors will also be >> > testing/optimising with this case too.
>> Does this really need to be SSD-specific? >> >> I hear that this (alignment) is high priority also for many >> of the big new disks, since they have 4k-byte sectors. >> Without better alignment, their performance will suffer, too. > > Well, one step at a time. We can detect SSD; can we detect those big new > disks (or, in general, the desired sector size)? Just to add to both points: quite a number of SSDs aren't compliant with the ATA-8 ACS [1], page 121 (see word 217). My OCZ Core SSD doesn't set word 217 to be 1 (it's reports 0 RPM, ie unset), thus 2.6.29-rc5 doesn't detect it as an SSD and thus set /sys/block/sda/queue/rotational to be 0. Here, perhaps it's just better to always align filesystems, which will help for RAID also. > Or are you saying that we should increase the alignment to 4KB in > general? It seems that SSDs actually really want 128KB, which starts to > feel like a bit much to apply to all disks: > > http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/ Alignment is suggested to increase the SSD's life too, so is a tiny space cost for other devices, so maybe it makes sense to do? Daniel --- [1] http://t13.org/Documents/UploadedDocuments/docs2007/D1699r4a-ATA8-ACS.pdf -- Daniel J Blueman _______________________________________________ parted-devel mailing list [email protected] http://lists.alioth.debian.org/mailman/listinfo/parted-devel
