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Diffstat (limited to 'Documentation/filesystems/ext4.txt')
| -rw-r--r-- | Documentation/filesystems/ext4.txt | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index cec829bc7291..97882df04865 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -85,7 +85,7 @@ Note: More extensive information for getting started with ext4 can be * extent format more robust in face of on-disk corruption due to magics, * internal redundancy in tree * improved file allocation (multi-block alloc) -* fix 32000 subdirectory limit +* lift 32000 subdirectory limit imposed by i_links_count[1] * nsec timestamps for mtime, atime, ctime, create time * inode version field on disk (NFSv4, Lustre) * reduced e2fsck time via uninit_bg feature @@ -100,6 +100,9 @@ Note: More extensive information for getting started with ext4 can be * efficent new ordered mode in JBD2 and ext4(avoid using buffer head to force the ordering) +[1] Filesystems with a block size of 1k may see a limit imposed by the +directory hash tree having a maximum depth of two. + 2.2 Candidate features for future inclusion * Online defrag (patches available but not well tested) @@ -180,8 +183,8 @@ commit=nrsec (*) Ext4 can be told to sync all its data and metadata performance. barrier=<0|1(*)> This enables/disables the use of write barriers in - the jbd code. barrier=0 disables, barrier=1 enables. - This also requires an IO stack which can support +barrier(*) the jbd code. barrier=0 disables, barrier=1 enables. +nobarrier This also requires an IO stack which can support barriers, and if jbd gets an error on a barrier write, it will disable again with a warning. Write barriers enforce proper on-disk ordering @@ -189,6 +192,9 @@ barrier=<0|1(*)> This enables/disables the use of write barriers in safe to use, at some performance penalty. If your disks are battery-backed in one way or another, disabling barriers may safely improve performance. + The mount options "barrier" and "nobarrier" can + also be used to enable or disable barriers, for + consistency with other ext4 mount options. inode_readahead=n This tuning parameter controls the maximum number of inode table blocks that ext4's inode @@ -310,6 +316,24 @@ journal_ioprio=prio The I/O priority (from 0 to 7, where 0 is the a slightly higher priority than the default I/O priority. +auto_da_alloc(*) Many broken applications don't use fsync() when +noauto_da_alloc replacing existing files via patterns such as + fd = open("foo.new")/write(fd,..)/close(fd)/ + rename("foo.new", "foo"), or worse yet, + fd = open("foo", O_TRUNC)/write(fd,..)/close(fd). + If auto_da_alloc is enabled, ext4 will detect + the replace-via-rename and replace-via-truncate + patterns and force that any delayed allocation + blocks are allocated such that at the next + journal commit, in the default data=ordered + mode, the data blocks of the new file are forced + to disk before the rename() operation is + commited. This provides roughly the same level + of guarantees as ext3, and avoids the + "zero-length" problem that can happen when a + system crashes before the delayed allocation + blocks are forced to disk. + Data Mode ========= There are 3 different data modes: |