Il 24/04/2013 14:12, Hannes Reinecke ha scritto: > On 04/24/2013 02:08 PM, Paolo Bonzini wrote: >> Il 24/04/2013 14:07, Hannes Reinecke ha scritto: >>> On 04/24/2013 01:17 PM, Paolo Bonzini wrote: >>>> Il 23/04/2013 22:07, James Bottomley ha scritto: >>>>> On Tue, 2013-04-23 at 15:41 -0400, Ric Wheeler wrote: >>>>>> For many years, we have used WCE as an indication that a device has a volatile >>>>>> write cache (not just a write cache) and used this as a trigger to send down >>>>>> SYNCHRONIZE_CACHE commands as needed. >>>>>> >>>>>> Some arrays with non-volatile cache seem to have WCE set and simply ignore the >>>>>> command. >>>>> >>>>> I bet they don't; they probably obey the spec. There's a SYNC_NV bit >>>>> which if unset (which it is in our implementation) means only sync your >>>>> non-NV cache. For a device with all NV, that equates to nop. >>>> >>>> Isn't it the other way round? >>>> >>>> SYNC_NV = 0 means "sync all your caches to the medium", and it's what we do. >>>> >>>> SYNC_NV = 1 means "sync volatile to non-volatile", and it's what Ric wants. >>>> >>>> So we should set SYNC_NV=1 if NV_SUP is set, perhaps only if the medium >>>> is non-removable just to err on the safe side. >>> >>> Or use 'WRITE_AND_VERIFY' here; that's guaranteed to hit the disk. >>> Plus it even has a guarantee about data consistency on the disk, >>> which the normal WRITE command has not. >> >> The point is to _avoid_ hitting the disk. :) >> > Ah. Really? > > Why do we discuss SYNCHRONIZE CACHE then? Because we do want the data to hit the non-volatile cache, just in case the disk has both a volatile and a non-volatile cache. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
