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| author |   Mingming Cao <cmm@us.ibm.com> | 2008-07-11 19:27:31 -0400 |
|---|---|---|
| committer |   Theodore Ts'o <tytso@mit.edu> | 2008-07-11 19:27:31 -0400 |
| commit | 49f1487b2e41bd8439ea39a4f15b4064e823cc54 (patch) | |
| tree | 03f6b923b8d1a2134b7049b199cce0244ce66fcf /Documentation/filesystems/ext4.txt | |
| parent | ext4: do not set extents feature from the kernel (diff) | |
| download | linux-dev-49f1487b2e41bd8439ea39a4f15b4064e823cc54.tar.xz linux-dev-49f1487b2e41bd8439ea39a4f15b4064e823cc54.zip | |
ext4: Documention update for new ordered mode and delayed allocation
Adding some documentations for delayed allocation and new ordered mode.
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'Documentation/filesystems/ext4.txt')
| -rw-r--r-- | Documentation/filesystems/ext4.txt | 21 |
1 files changed, 14 insertions, 7 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 7e940c64be47..80e193d82e2e 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -66,7 +66,7 @@ Mailing list: linux-ext4@vger.kernel.org * extent format reduces metadata overhead (RAM, IO for access, transactions) * extent format more robust in face of on-disk corruption due to magics, * internal redunancy in tree -* improved file allocation (multi-block alloc, delayed alloc) +* improved file allocation (multi-block alloc) * fix 32000 subdirectory limit * nsec timestamps for mtime, atime, ctime, create time * inode version field on disk (NFSv4, Lustre) @@ -77,6 +77,10 @@ Mailing list: linux-ext4@vger.kernel.org flex_bg feature * large file support * Inode allocation using large virtual block groups via flex_bg +* delayed allocation +* large block (up to pagesize) support +* efficent new ordered mode in JBD2 and ext4(avoid using buffer head to force + the ordering) 2.2 Candidate features for future inclusion @@ -239,7 +243,9 @@ stripe=n Number of filesystem blocks that mballoc will try to use for allocation size and alignment. For RAID5/6 systems this should be the number of data disks * RAID chunk size in file system blocks. - +delalloc (*) Deferring block allocation until write-out time. +nodelalloc Disable delayed allocation. Blocks are allocation + when data is copied from user to page cache. Data Mode ========= There are 3 different data modes: @@ -253,10 +259,10 @@ typically provide the best ext4 performance. * ordered mode In data=ordered mode, ext4 only officially journals metadata, but it logically -groups metadata and data blocks into a single unit called a transaction. When -it's time to write the new metadata out to disk, the associated data blocks -are written first. In general, this mode performs slightly slower than -writeback but significantly faster than journal mode. +groups metadata information related to data changes with the data blocks into a +single unit called a transaction. When it's time to write the new metadata +out to disk, the associated data blocks are written first. In general, +this mode performs slightly slower than writeback but significantly faster than journal mode. * journal mode data=journal mode provides full data and metadata journaling. All new data is @@ -264,7 +270,8 @@ written to the journal first, and then to its final location. In the event of a crash, the journal can be replayed, bringing both data and metadata into a consistent state. This mode is the slowest except when data needs to be read from and written to disk at the same time where it -outperforms all others modes. +outperforms all others modes. Curently ext4 does not have delayed +allocation support if this data journalling mode is selected. References ========== |