Hi all, [Topic] Barriers and SYNCHRONIZE CACHE [Abstract] In recent years some design flaws in the barriers implementation became apparent: - No indication about _which_ blocks to flush, so all outstanding blocks are flushed - No error handling for SYNCHRONIZE CACHE - SYNCHRONIZE CACHE affects all I/Os, so if a LUN is used by several virtual guests _all_ guests are affected - SYNCHRONIZE CACHE has a rather severe performance impact on RAID controllers (if executed directly) To overcome these issues I would propose to modify the barrier interface so that individual blocks can be marked as 'flushing'/'immediate'. This would allow the lower layers (eg. SCSI midlayer) to restrict the barriers operation on the affected blocks only. EG the SYNCHRONIZE_CACHE operation could be updated with a block list. Or more advanced methods (like FUA or tagging) could be used, avoiding the need to issue a SYNCHRONIZE CACHE altogether. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Markus Rex, HRB 16746 (AG Nürnberg) -- 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
