On Dec 17, 2013, at 8:11 AM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote: > On 12/17/13, 2:17 AM, Andreas Dilger wrote: >> The mke2fs(8) man page was updated in 4727c67dc2, but needs some >> more clear descriptions for extra_isize and metadta_csum features. >> The uninit_bg feature is supported by all ext4-capable kernels, >> and does have a slow e2fsck pass for newly-formatted filesystems, >> so remove the caveat. > > Looks ok to me, but I think there's still one thing missing; > it mentions metadata checksums but nothing in the manpage says > how to turn those on, AFAICT: Actually, the comments about metadata checksums is commented out in the man page. That isn't obvious at first glance. I had just seen it in the previous page, and the old description "a superset of the uninit_bg feature" wasn't very useful. As with anything, no complaints about the previous patch - it definitely improved the old content, and there is much more that needs to be done to document the metadata checksum feature (tune2fs, e2fsck, etc). Every bit helps. Cheers, Andreas > $ grep -i2 "checksum\|csum\|crc" misc/mke2fs.8 > .B uninit_bg > Create a filesystem without initializing all of the block groups. This > feature also enables checksums and highest-inode-used statistics in each > blockgroup. This feature can > speed up filesystem creation time noticeably (if lazy_itable_init is > > > (maybe I'm dense & missing it?) > > -Eric > >> Signed-off-by: Andreas Dilger <adilger@xxxxxxxxx> >> --- >> misc/mke2fs.8.in | 36 ++++++++++++++++++++++-------------- >> 1 files changed, 22 insertions(+), 14 deletions(-) >> >> diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in >> index df244de..4486014 100644 >> --- a/misc/mke2fs.8.in >> +++ b/misc/mke2fs.8.in >> @@ -210,8 +210,8 @@ in earlier versions of >> .BR mke2fs . >> The >> .B \-R >> -option is still accepted for backwards compatibility. The >> -following extended options are supported: >> +option is still accepted for backwards compatibility, but is deprecated. >> +The following extended options are supported: >> .RS 1.2i >> .TP >> .BI mmp_update_interval= interval >> @@ -548,7 +548,7 @@ of e2fsprogs will not support file systems with this feature enabled. >> .TP >> .B bigalloc >> .br >> -This feature enables clustered allocation, so that the unit of >> +This feature enables clustered block allocation, so that the unit of >> allocation is a power of two number of blocks. That is, each bit in the >> what had traditionally been known as the block allocation bitmap now >> indicates whether a cluster is in use or not, where a cluster is by >> @@ -570,7 +570,7 @@ features be enabled. >> .TP >> .B dir_index >> .br >> -Use hashed b-trees to speed up lookups in large directories. >> +Use hashed b-trees to speed up name lookups in large directories. >> .TP >> .B dir_nlink >> .br >> @@ -590,8 +590,15 @@ historical/backwards compatibility reasons.) >> .TP >> .B extra_isize >> .br >> -This feature enables storage of nanosecond timestamps and creation >> -time, if the inode size is larger than 256 bytes or larger. >> +This feature reserves a specific amount of space in each inode for >> +extended metadata such as nanosecond timestamps and file creation time, >> +even if the current kernel does not current need to reserve this much >> +space. Without this feature, the kernel will reserve the amount of >> +space for features currently it currently needs, and the rest may be >> +consumed by extended attributes. >> + >> +For this feature to be useful the inode size must be 256 bytes in size >> +or larger. >> .TP >> .B ext_attr >> .br >> @@ -649,10 +656,16 @@ set this feature automatically when a file > 2GiB is created.) >> .\" .TP >> .\" .B metadata_csum >> .\" .br >> -.\" Filesystem supports metadata checksumming. This feature enables a >> -.\" superset of the functionality of the >> +.\" Filesystem supports metadata checksumming. This feature stores >> +.\" checksums for all of the filesystem metadata (superblock, group >> +.\" descriptor blocks, inode and block bitmaps, directories, and >> +.\" extent tree blocks). The checksum algorithm used for the metadata >> +.\" blocks is different than the one used for group descriptors with the >> .\" .B uninit_bg >> -.\" feature. >> +.\" feature, these two features are incompatible and >> +.\" .B metadata_csum >> +.\" will be used preferentially instead of >> +.\" .BR uninit_bg . >> .\" .br >> .\" .B Future feature, available in e2fsprogs 1.43-WIP >> .TP >> @@ -719,11 +732,6 @@ and keep a high watermark for the unused inodes in a filesystem, to reduce >> .BR e2fsck (8) >> time. The result is that it can speed up filesystem creation time noticeably >> (if lazy_itable_init is enabled). >> -.IP >> -This first e2fsck run after enabling this feature will take the >> -full time, but subsequent e2fsck runs will take only a fraction of the >> -original time, depending on how full the file system is. >> -It is only supported by the ext4 filesystem in recent Linux kernels. >> .RE >> .TP >> .B \-q >> > Cheers, Andreas
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