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Accusys A12T3-Share User Manual
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5. RAIDUser GuidePage 4-9In the event of performance degradation or delay of a single drive due to aging, the RAIDsystem reads both data and parity stripes concurrently. It bypasses the slow reads and returnsdata to the host with the regenerated data and to provide stable performance based on theRAID parity.NoteSlow response of some hard disks can be tolerated in DLP mode, youmay use S.M.A.R.T. function to check the conditions of hard disks in anarray and replace the faulty ones.4.5.2 NCQNative Command Queuing (NCQ) is an extension of the Serial ATA protocol allowing hard diskdrives to internally optimize the order in which received read and write commands are executed.This can reduce the amount of unnecessary drive head movement, resulting in increasedperformance (and slightly decreased wear of the drive) for workloads where multiplesimultaneous read/write requests are outstanding.The figure above illustrates the access sequence in NCQ and non-NCQ mode. The contentsequences of the two hard disks are the same: 1, 2, 3, 4. However, the access sequence inNCQ mode may vary to improve the performance.4.5.3 SMART ModeS.M.A.R.T. is a monitoring system of disk drives to detect and report on various indicators ofreliability, in the hope of anticipating failure. Accusys RAID system supports S.M.A.R.T. Oncethis function is selected, you can select the check interval from the drop-down list. Choose from1 minute to 8 hours for SMART Mode to be active. The RAID controller will command each harddisk to perform S.M.A.R.T. according to the check interval selected. The check results will beshown as an Event message in the main menu.When running S.M.A.R.T. mode, the performance of the system will be slightly affected. Thehigher the check frequency, the more the sequential accesses are affected. It is recommendedto turn off S.M.A.R.T. if high performance required. On the other hand, running S.M.A.R.T.constantly allows you to monitor the conditions of hard disks at any time.The options of time to check disk’s S.M.A.R.T are 1,15,30,60 minutes and 2,4,8 hours. Westrongly suggest set to 8 hours. Frequently checking will reduce the life time of hard drives |
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