NEC S1300 User Manual

Also see for VERSA S1300 Series: User guide User guide Quick reference guide

Contents

NEC S1300 User Manual Manual pdf 19 page image

1-6 Disk Array Unit OverviewWrite Cache FeatureWith RAID level 5, the performance of the DAU may be decreased somewhat whenwriting small amounts of data to a disk. To increase performance, the DAU is equippedwith cache memory. When write data is stored in cache memory, the DAU mayterminate command processing and then write data to disks for improved performance.However, if the power is disrupted before the data in cache memory is written to disk,the data in the cache memory could be lost. To prevent this, the DAU power supplieseach include a battery backup unit to supply power to the cache memory, therebyretaining data in the cache memory should the power fail. The battery backup unit isfully charged after eight hours of operation.Cross Call FeatureBy using the cross call feature, logical disk drives can be accessed from alternativepaths within the DAU, even if a controller fails. The cross call feature minimizes serverdowntime thereby enhancing system performance. The cross call feature of the DAUcan be set with management software. The cross call feature has two states:! Off state In this state, the DAU is accessible only from the host adapter (HBA) ofthe bound host.! On state (shipping default) In this state, all logical drive numbers (LDNs) in theDAU are accessible from both controllers or one controller should one of thecontrollers fail.Note: Since one LDN is recognized from each controller, thiscross call must be used on the system where the logical disks can becontrolled exclusively. When you want to use the alternative pathswitching feature of the host, the cross call feature must be turnedon.Figure 1-2 illustrates a system connected to the DAU with the cross call feature turnedon and a failure with DAU controller HD#1.Figure 1-2. Cross Call Feature ConnectionsThis Manual:http://www.manuallib.com/nec/s1300ug-disk-array-unit-user-guide.html