On Wed, 10 Aug 2011, Ric Wheeler wrote: > On 08/10/2011 09:16 AM, Andreas Dilger wrote: > > On 2011-08-10, at 12:34 AM, Ric Wheeler wrote: > > > On 08/09/2011 06:52 PM, H. Peter Anvin wrote: > > > > Hi all, > > > > > > > > This is something I've wanted to see for a very long time, and it > > > > finally occurred to me that perhaps I should say something about it! > > > > > > > > It would be a very nice thing to have a flag to e2fsck, presumably -z, > > > > to zero out any unused data blocks, inodes and so on. The goal is to > > > > minimize the amount of space required after compressing a virtual disk > > > > image or similar, and to make sure any non-data isn't lying around. > > > Do you need it to be in the fsck tool? > > > > > > If you have a sparsely allocated block map under your file system, doing a > > > zero of all blocks could add hours for a big, slow S-ATA drives (2-3 hours > > > for a 1TB drive). > > I think Ted has a tool that does this already. It should be relatively > > simple oo do, like "dd if=/dev/zero of=/mountpoint/temp_zero_file&& rm > > /mountpoint/temp_zero_file. > > This will work but will be a potential multi-hour long process (and cause out > of space errors at some point for other applications for a very brief window > :)) > > > > > > An alternative for SSD's and devices that do TRIM/UNMAP would be to use > > > one of the batched discard tools (that would make discarded data read back > > > as zeroed). > > In fact, I thought Lukas has already made a tool for sending BLKDISCARD for > > all unused parts of the filesystem? > > > > Cheers, Andreas > > Right, I think he has. That tool (not part of fsck) would do the job much > quicker for enabled devices, You're right. It is a part of e2fsck and you can enable it with -E discard. Thanks! -Lukas -- 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
