diff options
| author | Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> | 2020-10-21 17:58:46 +0300 |
|---|---|---|
| committer | Max Reitz <mreitz@redhat.com> | 2020-12-18 12:35:55 +0100 |
| commit | 33fa2222eb044147e75e5ec395e1fd53328bc9fb (patch) | |
| tree | ab0ecf1c0054e6eefbbcad0d015c2b677e76f0ad /docs | |
| parent | 9530a25b8b7eb5cc1800b66ee617610cd43f0fad (diff) | |
block: introduce preallocate filter
It's intended to be inserted between format and protocol nodes to
preallocate additional space (expanding protocol file) on writes
crossing EOF. It improves performance for file-systems with slow
allocation.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201021145859.11201-9-vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
[mreitz: Two comment fixes, and bumped the version from 5.2 to 6.0]
Signed-off-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/system/qemu-block-drivers.rst.inc | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/docs/system/qemu-block-drivers.rst.inc b/docs/system/qemu-block-drivers.rst.inc index b052a6d14e..60a064b232 100644 --- a/docs/system/qemu-block-drivers.rst.inc +++ b/docs/system/qemu-block-drivers.rst.inc @@ -952,3 +952,29 @@ on host and see if there are locks held by the QEMU process on the image file. More than one byte could be locked by the QEMU instance, each byte of which reflects a particular permission that is acquired or protected by the running block driver. + +Filter drivers +~~~~~~~~~~~~~~ + +QEMU supports several filter drivers, which don't store any data, but perform +some additional tasks, hooking io requests. + +.. program:: filter-drivers +.. option:: preallocate + + The preallocate filter driver is intended to be inserted between format + and protocol nodes and preallocates some additional space + (expanding the protocol file) when writing past the file’s end. This can be + useful for file-systems with slow allocation. + + Supported options: + + .. program:: preallocate + .. option:: prealloc-align + + On preallocation, align the file length to this value (in bytes), default 1M. + + .. program:: preallocate + .. option:: prealloc-size + + How much to preallocate (in bytes), default 128M. |