Shingledmagneticrecording(SMR)caneffectivelyincreasethecapacityofharddiskdrives(HDDs).HostawareSMR(HA-SMR)isexpectedtobemorepopularthanotherSMRmodelsbecauseofitsbackwardcompatibilityandnewSMR-specificAPIs.However,anHA-SMRdriveoftensuffersperformancedegradationunderwrite-intensiveworkloadsbecauseoffrequentnon-sequentialwritesbufferedinthediskcache.Thenon-sequentialwritesmainlycomefromupdatewrites,smallrandomwritesandout-of-orderwrites.Inthispaper,weproposeahybridstoragesystemcalledROCOwhichaimstouseasolidstatedrive(SSD)cachetoimprovetheperformanceofanHA-SMRdrive.ROCOreordersout-of-orderwritesbelongingtothesamezoneandusestheSSDcachetoabsorbupdatewritesandsmallrandomwrites.WealsodesignadatareplacementalgorithmcalledCREAfortheSSDcache.CREAfirstconductszone-orientedhot/colddataidentificationtoidentifycold-cachedzonesandhot-cachedzones,andthenevictsdatablocksbelongingtocolderzoneswithhigherprioritiesthatcanbesequentiallywrittenorwrittenthroughhost-sideread-modify-writeoperations.Itgivesthelowestprioritytodatablocksbelongingtothehottest-cachedzonethathavetobenon-sequentiallywritten.ExperimentalresultsshowthatROCOcaneffectivelyreducenon-sequentialwritestotheHA-SMRdriveandimprovetheperformanceoftheHA-SMRdrive.
