diff options
-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 | |||
66 | * extent format reduces metadata overhead (RAM, IO for access, transactions) | 66 | * extent format reduces metadata overhead (RAM, IO for access, transactions) |
67 | * extent format more robust in face of on-disk corruption due to magics, | 67 | * extent format more robust in face of on-disk corruption due to magics, |
68 | * internal redunancy in tree | 68 | * internal redunancy in tree |
69 | * improved file allocation (multi-block alloc, delayed alloc) | 69 | * improved file allocation (multi-block alloc) |
70 | * fix 32000 subdirectory limit | 70 | * fix 32000 subdirectory limit |
71 | * nsec timestamps for mtime, atime, ctime, create time | 71 | * nsec timestamps for mtime, atime, ctime, create time |
72 | * inode version field on disk (NFSv4, Lustre) | 72 | * inode version field on disk (NFSv4, Lustre) |
@@ -77,6 +77,10 @@ Mailing list: linux-ext4@vger.kernel.org | |||
77 | flex_bg feature | 77 | flex_bg feature |
78 | * large file support | 78 | * large file support |
79 | * Inode allocation using large virtual block groups via flex_bg | 79 | * Inode allocation using large virtual block groups via flex_bg |
80 | * delayed allocation | ||
81 | * large block (up to pagesize) support | ||
82 | * efficent new ordered mode in JBD2 and ext4(avoid using buffer head to force | ||
83 | the ordering) | ||
80 | 84 | ||
81 | 2.2 Candidate features for future inclusion | 85 | 2.2 Candidate features for future inclusion |
82 | 86 | ||
@@ -239,7 +243,9 @@ stripe=n Number of filesystem blocks that mballoc will try | |||
239 | to use for allocation size and alignment. For RAID5/6 | 243 | to use for allocation size and alignment. For RAID5/6 |
240 | systems this should be the number of data | 244 | systems this should be the number of data |
241 | disks * RAID chunk size in file system blocks. | 245 | disks * RAID chunk size in file system blocks. |
242 | 246 | delalloc (*) Deferring block allocation until write-out time. | |
247 | nodelalloc Disable delayed allocation. Blocks are allocation | ||
248 | when data is copied from user to page cache. | ||
243 | Data Mode | 249 | Data Mode |
244 | ========= | 250 | ========= |
245 | There are 3 different data modes: | 251 | There are 3 different data modes: |
@@ -253,10 +259,10 @@ typically provide the best ext4 performance. | |||
253 | 259 | ||
254 | * ordered mode | 260 | * ordered mode |
255 | In data=ordered mode, ext4 only officially journals metadata, but it logically | 261 | In data=ordered mode, ext4 only officially journals metadata, but it logically |
256 | groups metadata and data blocks into a single unit called a transaction. When | 262 | groups metadata information related to data changes with the data blocks into a |
257 | it's time to write the new metadata out to disk, the associated data blocks | 263 | single unit called a transaction. When it's time to write the new metadata |
258 | are written first. In general, this mode performs slightly slower than | 264 | out to disk, the associated data blocks are written first. In general, |
259 | writeback but significantly faster than journal mode. | 265 | this mode performs slightly slower than writeback but significantly faster than journal mode. |
260 | 266 | ||
261 | * journal mode | 267 | * journal mode |
262 | data=journal mode provides full data and metadata journaling. All new data is | 268 | 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. | |||
264 | In the event of a crash, the journal can be replayed, bringing both data and | 270 | In the event of a crash, the journal can be replayed, bringing both data and |
265 | metadata into a consistent state. This mode is the slowest except when data | 271 | metadata into a consistent state. This mode is the slowest except when data |
266 | needs to be read from and written to disk at the same time where it | 272 | needs to be read from and written to disk at the same time where it |
267 | outperforms all others modes. | 273 | outperforms all others modes. Curently ext4 does not have delayed |
274 | allocation support if this data journalling mode is selected. | ||
268 | 275 | ||
269 | References | 276 | References |
270 | ========== | 277 | ========== |