HP P3410A HP NetRAID 1M/2M Installation & Configuration - Page 45

Chapter 4 Planning Write Policy ! When the IOP writes to disk, the data is first written to the cache on the assumption that the IOP will read it again soon. The two Write policies are: • Write-Through: In a write-through cache, data is written to disk at the same time it is cached. This setting provides better security because entries are always copied to disk. Unless an Uninterruptible Power Supply (like a battery backup unit) is connected, you should use the write-through setting, because otherwise data could be lost from cache memory in the event of a power failure. NOTE Write-Through is the recommended write policy for the HP NetRAID-1M adapter because this adapter does not have a battery backup unit. • Write-Back: In a write-back cache, data is written to disk only when it is forced out of the cache. Write-back is efficient, because an entry may be written many times in the cache without a disk access. Write-Back can be used if an Uninterruptible Power Supply maintains the data in cache memory in case of a power failure. NOTE Write-Back is NOT recommended unless one of the following is true: • The adapter is HP NetRAID-2M with a battery backup unit. • The system has an uninterruptible power supply (UPS). Write-Back is not certified for any logical drive used as a Novell NetWare volume. For each logical drive, record the write policy in Worksheet B. 37