> > EROS could do it, however.  EROS is an operating system that
> > automatically pages memory to disk as you run -- very OOZE-like!  EROS
> > is very careful in the order it saves things to disk; at any 
> > time, there is one complete and consistent snapshot, and one
> > snapshot being built. 
> 
The Rio Project (http://www.eecs.umich.edu/~pmchen/Rio/) seems to
be interesting:

 The Rio project is investigating how to implement and use reliable memory.
 Reliable memory enables dramatic improvements in reliability and
 performance.

 Major results to date include:

    * The Rio File Cache: We make ordinary main memory safe for persistent
 storage by enabling memory to survive operating system crashes. Rio survives
 crashes by protecting memory using virtual memory protection and restoring
 the data during the subsequent reboot. By eliminating reliability-induced
 disk writes, Rio performs 4-22 times as fast as a write-through file system
 and 2-14 times as fast as a standard Unix file system that loses 30 seconds
 of data on a crash. Rio is in production use as our project's file server
 and stores our mail and home directories. For more information, see our
 paper and slides from ASPLOS 1996.

    * The Vista Recoverable Memory: Transactions and recoverable memories
 are powerful mechanisms for handling failures and manipulating persistent
 data. Unfortunately, standard recoverable memories incur an overhead of
 several milliseconds per transaction. Vista improves transaction overhead by
 a factor of 2000. Of this factor of 2000, a factor of 20 is due to the Rio
 file cache, which absorbs synchronous writes to disk without losing data
 during system crashes. The remaining factor of 100 is due to Vista, a
 720-line recoverable-memory library tailored for Rio. Vista lowers
 transaction overhead to 5 microseconds by using no redo log, no system
 calls, and only one memory-to-memory copy. Here's a paper describing Vista
 that appeared in SOSP 1997.

    * Discount Checking: Discount Checking is a checkpointing library that
 allows general applications to recover from operating system and application
 crashes. Discount Checking builds on Rio's reliable main memory and Vista's
 fast transactions to achieve very low overhead and a high degree of
 transparency. Discount Checking slows real applications down by less than
 0.6%, even while taking checkpoints frequently enough to save every
 externally visible event. Discount Checking makes application and OS crashes
 appear as if the application pauses and resumes. We just wrote the following
 paper that describes Discount Checking.



-- 
Marcus Denker marcus at ira.uka.de  -- Squeak! http://squeakland.org