Difference between revisions of "Auto da alloc"
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<code>auto_da_alloc(*)</code> | <code>auto_da_alloc(*)</code> | ||
| − | + | Many broken applications don't use <code>[[fsync()]]</code> 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 committed. This provides roughly the same level of guarantees as <code>[[ext3]]</code>, and avoids the "zero-length" problem that can happen when a [[system crash]]es before the delayed allocation blocks are forced to disk. | |
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* {{mount}} | * {{mount}} | ||
* {{ext4}} | * {{ext4}} | ||
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| + | [[Category:Filesystem]] | ||
Latest revision as of 12:30, 26 November 2020
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 committed. 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.
See also[edit]
- File systems:
mount,umount,findmnt,find,swapon,swapoff,UUID, blkid, mount options:/etc/fstab,udisksctl mount,guestmount,/proc/mounts,fstrim,systemd-mount,defaults ext4e2fsck,,fsck.ext4, superblock, inode, block size, mkfs.ext4 tune2fswipefs,resize2fsstat,extents, Review ext4 journalctl logs. Read-only file system,virt-resize, ACL
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