diff options
Diffstat (limited to 'Documentation/filesystems/ceph.txt')
| -rw-r--r-- | Documentation/filesystems/ceph.txt | 186 |
1 files changed, 0 insertions, 186 deletions
diff --git a/Documentation/filesystems/ceph.txt b/Documentation/filesystems/ceph.txt deleted file mode 100644 index b19b6a03f91c..000000000000 --- a/Documentation/filesystems/ceph.txt +++ /dev/null @@ -1,186 +0,0 @@ -Ceph Distributed File System -============================ - -Ceph is a distributed network file system designed to provide good -performance, reliability, and scalability. - -Basic features include: - - * POSIX semantics - * Seamless scaling from 1 to many thousands of nodes - * High availability and reliability. No single point of failure. - * N-way replication of data across storage nodes - * Fast recovery from node failures - * Automatic rebalancing of data on node addition/removal - * Easy deployment: most FS components are userspace daemons - -Also, - * Flexible snapshots (on any directory) - * Recursive accounting (nested files, directories, bytes) - -In contrast to cluster filesystems like GFS, OCFS2, and GPFS that rely -on symmetric access by all clients to shared block devices, Ceph -separates data and metadata management into independent server -clusters, similar to Lustre. Unlike Lustre, however, metadata and -storage nodes run entirely as user space daemons. File data is striped -across storage nodes in large chunks to distribute workload and -facilitate high throughputs. When storage nodes fail, data is -re-replicated in a distributed fashion by the storage nodes themselves -(with some minimal coordination from a cluster monitor), making the -system extremely efficient and scalable. - -Metadata servers effectively form a large, consistent, distributed -in-memory cache above the file namespace that is extremely scalable, -dynamically redistributes metadata in response to workload changes, -and can tolerate arbitrary (well, non-Byzantine) node failures. The -metadata server takes a somewhat unconventional approach to metadata -storage to significantly improve performance for common workloads. In -particular, inodes with only a single link are embedded in -directories, allowing entire directories of dentries and inodes to be -loaded into its cache with a single I/O operation. The contents of -extremely large directories can be fragmented and managed by -independent metadata servers, allowing scalable concurrent access. - -The system offers automatic data rebalancing/migration when scaling -from a small cluster of just a few nodes to many hundreds, without -requiring an administrator carve the data set into static volumes or -go through the tedious process of migrating data between servers. -When the file system approaches full, new nodes can be easily added -and things will "just work." - -Ceph includes flexible snapshot mechanism that allows a user to create -a snapshot on any subdirectory (and its nested contents) in the -system. Snapshot creation and deletion are as simple as 'mkdir -.snap/foo' and 'rmdir .snap/foo'. - -Ceph also provides some recursive accounting on directories for nested -files and bytes. That is, a 'getfattr -d foo' on any directory in the -system will reveal the total number of nested regular files and -subdirectories, and a summation of all nested file sizes. This makes -the identification of large disk space consumers relatively quick, as -no 'du' or similar recursive scan of the file system is required. - -Finally, Ceph also allows quotas to be set on any directory in the system. -The quota can restrict the number of bytes or the number of files stored -beneath that point in the directory hierarchy. Quotas can be set using -extended attributes 'ceph.quota.max_files' and 'ceph.quota.max_bytes', eg: - - setfattr -n ceph.quota.max_bytes -v 100000000 /some/dir - getfattr -n ceph.quota.max_bytes /some/dir - -A limitation of the current quotas implementation is that it relies on the -cooperation of the client mounting the file system to stop writers when a -limit is reached. A modified or adversarial client cannot be prevented -from writing as much data as it needs. - -Mount Syntax -============ - -The basic mount syntax is: - - # mount -t ceph monip[:port][,monip2[:port]...]:/[subdir] mnt - -You only need to specify a single monitor, as the client will get the -full list when it connects. (However, if the monitor you specify -happens to be down, the mount won't succeed.) The port can be left -off if the monitor is using the default. So if the monitor is at -1.2.3.4, - - # mount -t ceph 1.2.3.4:/ /mnt/ceph - -is sufficient. If /sbin/mount.ceph is installed, a hostname can be -used instead of an IP address. - - - -Mount Options -============= - - ip=A.B.C.D[:N] - Specify the IP and/or port the client should bind to locally. - There is normally not much reason to do this. If the IP is not - specified, the client's IP address is determined by looking at the - address its connection to the monitor originates from. - - wsize=X - Specify the maximum write size in bytes. Default: 16 MB. - - rsize=X - Specify the maximum read size in bytes. Default: 16 MB. - - rasize=X - Specify the maximum readahead size in bytes. Default: 8 MB. - - mount_timeout=X - Specify the timeout value for mount (in seconds), in the case - of a non-responsive Ceph file system. The default is 30 - seconds. - - caps_max=X - Specify the maximum number of caps to hold. Unused caps are released - when number of caps exceeds the limit. The default is 0 (no limit) - - rbytes - When stat() is called on a directory, set st_size to 'rbytes', - the summation of file sizes over all files nested beneath that - directory. This is the default. - - norbytes - When stat() is called on a directory, set st_size to the - number of entries in that directory. - - nocrc - Disable CRC32C calculation for data writes. If set, the storage node - must rely on TCP's error correction to detect data corruption - in the data payload. - - dcache - Use the dcache contents to perform negative lookups and - readdir when the client has the entire directory contents in - its cache. (This does not change correctness; the client uses - cached metadata only when a lease or capability ensures it is - valid.) - - nodcache - Do not use the dcache as above. This avoids a significant amount of - complex code, sacrificing performance without affecting correctness, - and is useful for tracking down bugs. - - noasyncreaddir - Do not use the dcache as above for readdir. - - noquotadf - Report overall filesystem usage in statfs instead of using the root - directory quota. - - nocopyfrom - Don't use the RADOS 'copy-from' operation to perform remote object - copies. Currently, it's only used in copy_file_range, which will revert - to the default VFS implementation if this option is used. - - recover_session=<no|clean> - Set auto reconnect mode in the case where the client is blacklisted. The - available modes are "no" and "clean". The default is "no". - - * no: never attempt to reconnect when client detects that it has been - blacklisted. Operations will generally fail after being blacklisted. - - * clean: client reconnects to the ceph cluster automatically when it - detects that it has been blacklisted. During reconnect, client drops - dirty data/metadata, invalidates page caches and writable file handles. - After reconnect, file locks become stale because the MDS loses track - of them. If an inode contains any stale file locks, read/write on the - inode is not allowed until applications release all stale file locks. - -More Information -================ - -For more information on Ceph, see the home page at - https://ceph.com/ - -The Linux kernel client source tree is available at - https://github.com/ceph/ceph-client.git - git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client.git - -and the source for the full system is at - https://github.com/ceph/ceph.git |