> > Pay attention to vtsync? May be not for your mythical multiTB > > ramflash but in real life syncing on every write is expensive. > > are you sure? On a multicore server, why not have a syncing task and a > serving task? Since all of the arena is in ram, the synciing task will > not interfere with the serving task, esp. if sata controller and > network are on different PCI busses. > > I don't think the tradeoffs are obvious at all.
that doesn't sound synchronous to me. what i think of when i think of flush on write is that the i/o is done before the reply to the write. this has two implications, there's no way to do any elevatoring, and you take a full round-trip to the disk delay for each write, no amortization is possible. i would think that the client is in the best position to tell the storage when things must be flushed. it might be best to only write when told to flush and do so in such a way that it's clear if the transaction has finished. that way, if you're really careful and flush caches down to the storage media, you can recover if things go sideways. - erik
