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Diffstat (limited to 'Documentation/device-mapper/writecache.txt')
| -rw-r--r-- | Documentation/device-mapper/writecache.txt | 70 |
1 files changed, 0 insertions, 70 deletions
diff --git a/Documentation/device-mapper/writecache.txt b/Documentation/device-mapper/writecache.txt deleted file mode 100644 index 01532b3008ae..000000000000 --- a/Documentation/device-mapper/writecache.txt +++ /dev/null @@ -1,70 +0,0 @@ -The writecache target caches writes on persistent memory or on SSD. It -doesn't cache reads because reads are supposed to be cached in page cache -in normal RAM. - -When the device is constructed, the first sector should be zeroed or the -first sector should contain valid superblock from previous invocation. - -Constructor parameters: -1. type of the cache device - "p" or "s" - p - persistent memory - s - SSD -2. the underlying device that will be cached -3. the cache device -4. block size (4096 is recommended; the maximum block size is the page - size) -5. the number of optional parameters (the parameters with an argument - count as two) - start_sector n (default: 0) - offset from the start of cache device in 512-byte sectors - high_watermark n (default: 50) - start writeback when the number of used blocks reach this - watermark - low_watermark x (default: 45) - stop writeback when the number of used blocks drops below - this watermark - writeback_jobs n (default: unlimited) - limit the number of blocks that are in flight during - writeback. Setting this value reduces writeback - throughput, but it may improve latency of read requests - autocommit_blocks n (default: 64 for pmem, 65536 for ssd) - when the application writes this amount of blocks without - issuing the FLUSH request, the blocks are automatically - commited - autocommit_time ms (default: 1000) - autocommit time in milliseconds. The data is automatically - commited if this time passes and no FLUSH request is - received - fua (by default on) - applicable only to persistent memory - use the FUA flag - when writing data from persistent memory back to the - underlying device - nofua - applicable only to persistent memory - don't use the FUA - flag when writing back data and send the FLUSH request - afterwards - - some underlying devices perform better with fua, some - with nofua. The user should test it - -Status: -1. error indicator - 0 if there was no error, otherwise error number -2. the number of blocks -3. the number of free blocks -4. the number of blocks under writeback - -Messages: - flush - flush the cache device. The message returns successfully - if the cache device was flushed without an error - flush_on_suspend - flush the cache device on next suspend. Use this message - when you are going to remove the cache device. The proper - sequence for removing the cache device is: - 1. send the "flush_on_suspend" message - 2. load an inactive table with a linear target that maps - to the underlying device - 3. suspend the device - 4. ask for status and verify that there are no errors - 5. resume the device, so that it will use the linear - target - 6. the cache device is now inactive and it can be deleted |