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. :) Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
