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Troubleshooting
13. Reduce the impact of background task
The background I/O tasks, like RAID initialization or rebuilding, have
impact to the performance of your applications, because they need to
access hard disks. Even SMART monitoring could cause disturbance. You
may set the priority of background tasks to low, or schedule these tasks to
run at non-business hours to avoid the impact.
14. Constantly monitor the I/O statistics
To know details of the performance of your RAID system, you may check
the performance management web pages, by which you may identify
slow hard disks, slow host interface links, or unbalanced workload
distribution (see 2.11 Performance Management on page 2-76). Some
operating systems offer similar utilities. For example, Microsoft Windows
Performance Monitor not only displays many useful statistics but also can
be configured to send out alerts according to the threshold you set. The
statistics can also be saved as a log file. You may find similar utilities from
your HBA and switch vendors.
15. Know more about performance benchmarking
And finally, you have to understand that the test result of performance
benchmark tool is not always related to your real-world performance.
You have to be careful with choose right tools and right testing workload
profiles to mimic your application behaviors.
6.4 Hard Disks
Hard disks are the most important components in a RAID system because
they are where the data resides. Please contact your RAID system
supplier to get the list of qualified hard disk models when you’re choosing
hard disks.
1. Hard disks cannot be recognized by the RAID controller
The hard disks are initialized by the RAID controller when the controller
boots up or when the hard disks are plugged into the RAID system. If a
hard disk cannot be ready within a specific period of time during the
initialization, the RAID controller will force the hard disks enter faulty state
and you cannot see any model information of hard disks. To ensure hard
disks have enough time for power-on, you may extend the delay time
when boot-up of the RAID controller (see 2.8.1 Hard disks on page 2-56).
2. Hard disks are offline unexpected
The RAID controller takes a hard disk offline when the hard disk cannot
respond to the RAID controller after the full-cycle error recovery
procedure has been done. This could happen when the hard disk is
permanently dead because of its internal component failure, and you
lose all your data on the hard disk. Another reason a hard disk is taken
offline is that its reserved space for meta-data (RAID configurations)
cannot be written, which means the reserved space for bad block
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