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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>
This commit is contained in:
Mingming Cao 2008-07-11 19:27:31 -04:00 committed by Theodore Ts'o
parent e4079a11f5
commit 49f1487b2e
1 changed files with 14 additions and 7 deletions
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21
Documentation/filesystems/ext4.txt
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@ -66,7 +66,7 @@ Mailing list: linux-ext4@vger.kernel.org
* extent format reduces metadata overhead (RAM, IO for access, transactions) * extent format reduces metadata overhead (RAM, IO for access, transactions)
* extent format more robust in face of on-disk corruption due to magics, * extent format more robust in face of on-disk corruption due to magics,
* internal redunancy in tree * internal redunancy in tree
* improved file allocation (multi-block alloc, delayed alloc) * improved file allocation (multi-block alloc)
* fix 32000 subdirectory limit * fix 32000 subdirectory limit
* nsec timestamps for mtime, atime, ctime, create time * nsec timestamps for mtime, atime, ctime, create time
* inode version field on disk (NFSv4, Lustre) * inode version field on disk (NFSv4, Lustre)
@ -77,6 +77,10 @@ Mailing list: linux-ext4@vger.kernel.org
flex_bg feature flex_bg feature
* large file support * large file support
* Inode allocation using large virtual block groups via flex_bg * 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 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 to use for allocation size and alignment. For RAID5/6
systems this should be the number of data systems this should be the number of data
disks * RAID chunk size in file system blocks. 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 Data Mode
========= =========
There are 3 different data modes: There are 3 different data modes:
@ -253,10 +259,10 @@ typically provide the best ext4 performance.
* ordered mode * ordered mode
In data=ordered mode, ext4 only officially journals metadata, but it logically 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 groups metadata information related to data changes with the data blocks into a
it's time to write the new metadata out to disk, the associated data blocks single unit called a transaction. When it's time to write the new metadata
are written first. In general, this mode performs slightly slower than out to disk, the associated data blocks are written first. In general,
writeback but significantly faster than journal mode. this mode performs slightly slower than writeback but significantly faster than journal mode.
* journal mode * journal mode
data=journal mode provides full data and metadata journaling. All new data is 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 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 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 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 References
========== ==========