--- /dev/null
+config DST
+ tristate "Distributed storage"
+ depends on NET && CRYPTO && SYSFS && BLK_DEV
+ select CONNECTOR
+ ---help---
+ DST is a network block device storage, which can be used to organize
+ exported storage on the remote nodes into the local block device.
+
+ DST works on top of any network media and protocol; it is just a matter
+ of configuration utility to understand the correct addresses. The most
+ common example is TCP over IP, which allows to pass through firewalls and
+ create remote backup storage in a different datacenter. DST requires
+ single port to be enabled on the exporting node and outgoing connections
+ on the local node.
+
+ DST works with in-kernel client and server, which improves performance by
+ eliminating unneded data copies and by not depending on the version
+ of the external IO components. It requires userspace configuration utility
+ though.
+
+ DST uses transaction model, when each store has to be explicitly acked
+ from the remote node to be considered as successfully written. There
+ may be lots of in-flight transactions. When remote host does not ack
+ the transaction it will be resent predefined number of times with specified
+ timeouts between them. All those parameters are configurable. Transactions
+ are marked as failed after all resends complete unsuccessfully; having
+ long enough resend timeout and/or large number of resends allows not to
+ return error to the higher (FS usually) layer in case of short network
+ problems or remote node outages. In case of network RAID setup this means
+ that storage will not degrade until transactions are marked as failed, and
+ thus will not force checksum recalculation and data rebuild. In case of
+ connection failure DST will try to reconnect to the remote node automatically.
+ DST sends ping commands at idle time to detect if remote node is alive.
+
+ Because of transactional model it is possible to use zero-copy sending
+ without worry of data corruption (which in turn could be detected by the
+ strong checksums though).
+
+ DST may fully encrypt the data channel in case of untrusted channel and implement
+ strong checksum of the transferred data. It is possible to configure algorithms
+ and crypto keys; they should match on both sides of the network channel.
+ Crypto processing does not introduce noticeble performance overhead, since DST
+ uses configurable pool of threads to perform crypto processing.
+
+ DST utilizes memory pool model of all its transaction allocations (it is the
+ only additional allocation on the client) and server allocations (bio pools,
+ while pages are allocated from the slab).
+
+ At startup DST performs a simple negotiation with the export node to determine
+ access permissions and size of the exported storage. It can be extended if
+ new parameters should be autonegotiated.
+
+ DST carries block IO flags in the protocol, which allows to transparently implement
+ barriers and sync/flush operations. Those flags are used in the export node where
+ IO against the local storage is performed, which means that sync write will be sync
+ on the remote node too, which in turn improves data integrity and improved resistance
+ to errors and data corruption during power outages or storage damages.
+
+ Homepage: http://www.ioremap.net/projects/dst
+ Userspace configuration utility and the latest releases: http://www.ioremap.net/archive/dst/
+
+config DST_DEBUG
+ bool "DST debug"
+ depends on DST
+ ---help---
+ This option will enable HEAVY debugging of the DST.
+ Turn it on ONLY if you have to debug some really obscure problem.
projects / linux-2.6-omap-h63xx.git / blobdiff