On Wed, Nov 24, 2010 at 9:48 PM, Mark Lord <kernel@xxxxxxxxxxxx> wrote: > On 10-11-19 11:30 AM, Ted Ts'o wrote: >> >> On Fri, Nov 19, 2010 at 04:44:33PM +0100, Lukas Czerner wrote: >>>> >>>> But, oddly, it _is_ the default for mke2fs -t ext4, >>>> which really threw me for a loop recently. >>>> >>>> I though my system had locked up when suddenly everything >>>> went dead for a very long time (many minutes) while installing a >>>> new system. >> >> Yeah, the assumption was doing a single big discard (which is all >> mke2fs is doing) should be fast. At least on sanely implemented SSD's >> (i.e., like the Intel X25-M) it should be, since all that should >> require is a flash write to the global mapping table, declaring all of >> the blocks as free. > > But mke2fs probably is NOT doing a "single big discard", because for SATA > the > TRIM command is limited to 64K sectors per range.. and the in-kernel TRIM > code only ever does single ranges.. > > So doing a discard over an entire drive-encompassing partition, say.. 100GB, > will require 3000+ individual TRIM commands. At (say) 200msecs each, that > adds up to about ten minutes of execution time. Or less if the drive is > faster than that. > > Whereas.. grouping them into 64-ranges per trim, could reduce the execution > time down to perhaps 1/50th of that, or in the range of 10-20 seconds > instead. > > Cheers Mark, With recent kernels, this is supposed to work as you describe. ie. 64 contiguous ranges per trim command. If you see a significant speed difference between mke2fs and running wiper.sh on that same filesystem immediately after formatting, then their is likely a bug worth chasing. Are you seeing an actual speed difference, or just assuming there is one? If mke2fs is slower than wiper.sh, what kernel are you testing with? Greg -- Greg Freemyer Head of EDD Tape Extraction and Processing team Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer CNN/TruTV Aired Forensic Imaging Demo - http://insession.blogs.cnn.com/2010/03/23/how-computer-evidence-gets-retrieved/ The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
