2 tristate "Distributed storage"
3 depends on NET && CRYPTO && SYSFS
7 DST is a network block device storage, which can be used to organize
8 exported storages on the remote nodes into the local block device.
10 DST is a network block device storage, which can be used to organize
11 exported storages on the remote nodes into the local block device.
13 DST works on top of any network media and protocol, it is just a matter
14 of configuration utility to understand the correct addresses. The most
15 common example is TCP over IP allows to pass through firewalls and
16 created remote backup storage in the different datacenter. DST requires
17 single port to be enabled on the exporting node and outgoing connections
20 DST works with in-kernel client and server, which improves the performance
21 eliminating unneded data copies and allows not to depend on the version
22 of the external IO components. It requires userspace configuration utility
25 DST uses transaction model, when each store has to be explicitly acked
26 from the remote node to be considered as successfully written. There
27 may be lots of in-flight transactions. When remote host does not ack
28 the transaction it will be resent predefined number of times with specified
29 timeouts between them. All those parameters are configurable. Transactions
30 are marked as failed after all resends completed unsuccessfully, having
31 long enough resend timeout and/or large number of resends allows not to
32 return error to the higher (FS usually) layer in case of short network
33 problems or remote node outages. In case of network RAID setup this means
34 that storage will not degrade until transactions are marked as failed, and
35 thus will not force checksum recalculation and data rebuild. In case of
36 connection failure DST will try to reconnect to the remote node automatically.
37 DST sends ping commands at idle time to detect if remote node is alive.
39 Because of transactional model it is possible to use zero-copy sending
40 without worry of data corruption (which in turn could be detected by the
41 strong checksums though).
43 DST may fully encrypt the data channel in case of untrusted channel and implement
44 strong checksum of the transferred data. It is possible to configure algorithms
45 and crypto keys, they should match on both sides of the network channel.
46 Crypto processing does not introduce noticeble performance overhead, since DST
47 uses configurable pool of threads to perform crypto processing.
49 DST utilizes memory pool model of all its transaction allocations (it is the
50 only additional allocation on the client) and server allocations (bio pools,
51 while pages are allocated from the slab).
53 At startup DST performs a simple negotiation with the export node to determine
54 access permissions and size of the exported storage. It can be extended if
55 new parameters should be autonegotiated.
57 DST carries block IO flags in the protocol, which allows to transparently implement
58 barriers and sync/flush operations. Those flags are used in the export node where
59 IO against the local storage is performed, which means that sync write will be sync
60 on the remote node too, which in turn improves data integrity and improved resistance
61 to errors and data corruption during power outages or storage damages.
63 Homepage: http://www.ioremap.net/projects/dst
64 Userspace configuration utility and the latest releases: http://www.ioremap.net/archive/dst/
70 This option will turn HEAVY debugging of the DST.
71 Turn it on ONLY if you have to debug some really obscure problem.