RAID Maintenance Free Backup Basic Functionality (RMFBU)

RAIDMaintenanceFreeBackupBasicFunctionality
3

occursandthearraysaresetinwrite‐backmode.Transferofcachememoryisaccomplishedusingdual
USBconnectionsbetweentheraidcontroller/module’sROCchipUSBportandtheUSBportonthe
TFM’scachecontrollerchip.Thesuper‐capacitorpackcan
holdthememorycircuitatvoltagelong
enoughforthedatatobecopiedfromcontrollercachetoTFMflash. Thecapacitorstakeapproximately
2minutesatpowerontocharge,andcapacitorchargeismaintainedviaaconstantsmalltricklecharge.
Alearncycleisinitiatedfollowingthepoweron
andchargingoftheRMFBU.Thelearncycleallows the
TFMgasgaugecircuitrytocalibratetheoperationofthesuper‐capacitorpackandtojudgethecharge
levelanddischargecapacity.Duringalearncyclethesuper‐capacitorpackisdischargedbyabout30%
andthenrechargedtoslightly
above100%capacity,thegasgaugethenmeasuresdischargeovertime
andmakesanestimateofthehealthofthesuper‐capacitorpack.Duringalearncycle,thesuper‐
capacitorisnotdischargedbelowthelevelneededtomaintainacacheoffloadoperation(moving
cacheddatafromcontrollerDDRmemoryto
NANDflashmemoryontheTFM)intheeventofapower
outageduringthelearncycleprocess.ThecontrollerfirmwarecontinuestomonitortheTFMtomanage
theuseofwritebackraidvolumemode.
Thefirmwarewaitsfor5minutesafterbootbeforethelearncycleisinitiated.
AnewRMFBUwill
undergoapproximately5minutesofchargeand dischargecyclesduringfirsttimeuse.ARMFBU
previouslyusedinthesystemwillundergoasinglelearncyclefollowingpoweron.Thelearncyclemust
completebeforetheraidcontroller’s storagevolumesareallowedtoruninwriteback
cachemode
unlessthe“alwayswriteback”settingisselectedintheraidvolumecachepropertiessettingin
controller/modulefirmware.Learncycleswillberepeatedonascheduledbasis.Thedefault learncycle
scheduleisonceevery28days,thissettingcanbeadjustedbyusingoneofthecontroller
management
utilitiessuchasRaidWebConsole2,ortheCommandTool2/StorCliutility.
Uponalossofpower,theraidcontrollersensesthelossofpowerandswitchesthememorycircuitto
drawpowerfromthesuper‐capacitors,oncethefirmwaredeterminesthatthetransferofpowersource
iscomplete,
itwillcopydataincachethathasnotbeenwrittentodiskdrives(dirtycache)fro mthe
controllersDDRmemorytotheTFM’sNANDflashmemory(acache‐offload).

Figure3‐CacheOffload
Oncepowerisrestored,theraidcontrollerfirmwaredeterminesifacacheoffloadtookplaceby
checkingfora“dirtycache”bitsetinafirmwareregister.Ifitfindsthatacacheoffloadtookplace,the
raidcontrollerwillthencopytheflashcontentsbacktocontrollercachememory.This
processhappens