On Fri, 01 Jun 2007 16:16:01 +0900, Tejun Heo said: > Don't those thingies usually have NV cache or backed by battery such > that ORDERED_DRAIN is enough?
Probably *most* do, but do you really want to bet the user's data on it? > The problem is that the interface between the host and a storage device > (ATA or SCSI) is not built to communicate that kind of information > (grouped flush, relaxed ordering...). I think battery backed > ORDERED_DRAIN combined with fine-grained host queue flush would be > pretty good. It doesn't require some fancy new interface which isn't > gonna be used widely anyway and can achieve most of performance gain if > the storage plays it smart. Yes, that would probably be "pretty good". But how do you get the storage device to *reliably* tell the truth about what it actually implements? (Consider the number of devices that downright lie about their implementation of cache flushing....)
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