1config DST 2 tristate "Distributed storage" 3 depends on NET && CRYPTO && SYSFS && BLK_DEV 4 select CONNECTOR 5 ---help--- 6 DST is a network block device storage, which can be used to organize 7 exported storage on the remote nodes into the local block device. 8 9 DST works on top of any network media and protocol; it is just a matter 10 of configuration utility to understand the correct addresses. The most 11 common example is TCP over IP, which allows to pass through firewalls and 12 create remote backup storage in a different datacenter. DST requires 13 single port to be enabled on the exporting node and outgoing connections 14 on the local node. 15 16 DST works with in-kernel client and server, which improves performance by 17 eliminating unneded data copies and by not depending on the version 18 of the external IO components. It requires userspace configuration utility 19 though. 20 21 DST uses transaction model, when each store has to be explicitly acked 22 from the remote node to be considered as successfully written. There 23 may be lots of in-flight transactions. When remote host does not ack 24 the transaction it will be resent predefined number of times with specified 25 timeouts between them. All those parameters are configurable. Transactions 26 are marked as failed after all resends complete unsuccessfully; having 27 long enough resend timeout and/or large number of resends allows not to 28 return error to the higher (FS usually) layer in case of short network 29 problems or remote node outages. In case of network RAID setup this means 30 that storage will not degrade until transactions are marked as failed, and 31 thus will not force checksum recalculation and data rebuild. In case of 32 connection failure DST will try to reconnect to the remote node automatically. 33 DST sends ping commands at idle time to detect if remote node is alive. 34 35 Because of transactional model it is possible to use zero-copy sending 36 without worry of data corruption (which in turn could be detected by the 37 strong checksums though). 38 39 DST may fully encrypt the data channel in case of untrusted channel and implement 40 strong checksum of the transferred data. It is possible to configure algorithms 41 and crypto keys; they should match on both sides of the network channel. 42 Crypto processing does not introduce noticeble performance overhead, since DST 43 uses configurable pool of threads to perform crypto processing. 44 45 DST utilizes memory pool model of all its transaction allocations (it is the 46 only additional allocation on the client) and server allocations (bio pools, 47 while pages are allocated from the slab). 48 49 At startup DST performs a simple negotiation with the export node to determine 50 access permissions and size of the exported storage. It can be extended if 51 new parameters should be autonegotiated. 52 53 DST carries block IO flags in the protocol, which allows to transparently implement 54 barriers and sync/flush operations. Those flags are used in the export node where 55 IO against the local storage is performed, which means that sync write will be sync 56 on the remote node too, which in turn improves data integrity and improved resistance 57 to errors and data corruption during power outages or storage damages. 58 59 Homepage: http://www.ioremap.net/projects/dst 60 Userspace configuration utility and the latest releases: http://www.ioremap.net/archive/dst/ 61 62config DST_DEBUG 63 bool "DST debug" 64 depends on DST 65 ---help--- 66 This option will enable HEAVY debugging of the DST. 67 Turn it on ONLY if you have to debug some really obscure problem. 68