On 2012-06-26, at 12:07, "Nelson, John R" <John_Nelson@xxxxxxxxxxxxxxx> wrote: > ok i see! > So when there are like > 3/3/4 that means double index blocks?? How many extents can a single extent index hold in a block? The header takes 12 bytes, and each extent or index pointer takes 12 bytes, so for 4kB blocksize there can be (4096 / 12) - 1 = 340 extents per block. The maximum extent size for 4kB blocks is 2^15*4kB = 128MB, so each index block can map up to ~42GB, so a two-level tree can map just over 14TB under ideal conditions. Cheers, Andreas > ________________________________________ > From: Andreas Dilger [adilger@xxxxxxxxx] > Sent: Tuesday, June 26, 2012 11:40 AM > To: Nelson, John R > Cc: linux-ext4@xxxxxxxxxxxxxxx > Subject: Re: Extent Depth Histogram Fsck > > On 2012-06-26, at 8:34 AM, Nelson, John R wrote: >> What does the extent depth histogram mean? Is it a measure of something? >> >> like mine is >> >> >> Extent depth histogram: 36010/81 > > This means that of all the extent-mapped files in the filesystem, > 36010 files have an extent tree of depth 0 (i.e. they fit inside the inode) > 81 files have an extent tree of depth 1 (i.e. there is a single index block) > > Typically, files larger than 4 * 128MB = 512MB need an index block, but if > the maximum-sized extents cannot be allocated then an index block will be needed for smaller files. Only if you have very large files (> 40GB), > or a very fragmented free space would you need more than a single level > of index blocks. > > Cheers, Andreas > > > > > > > -- 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
