HP Surestore Disk Array FC60 Disk Array FC60 User's Guide (A5635A) - Page 125

Cache read ahead prefetch

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Setting: Cache read ahead (prefetch) Function: Sets the number of additional sequential blocks transferred into read cache each time a read I/O is performed. Read ahead can be set for each volume. Performance Impact: Read ahead can significantly improve read performance for sequential I/O transactions. When a read is performed, the specified number of additional blocks are also read into cache in anticipation of the host issuing a read request for that data. Because the data is in cache, the number of read hits increases, improving performance. Read ahead is useful only for sequential I/O profiles. Read ahead can be tuned by increasing the setting and monitoring the cache hit percentage. If the percentage improves, the setting can be increased again until no improvement in performance is seen. 125 Managing the Disk Array

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125
Managing the Disk Array
Setting:
Cache read ahead (prefetch)
Function:
Sets the number of additional sequential blocks transferred into read cache each time
a read I/O is performed. Read ahead can be set for each volume.
Performance Impact:
Read ahead can significantly improve read performance for sequential
I/O transactions. When a read is performed, the specified number of additional blocks are also
read into cache in anticipation of the host issuing a read request for that data. Because the data
is in cache, the number of read hits increases, improving performance. Read ahead is useful only
for sequential I/O profiles.
Read ahead can be tuned by increasing the setting and monitoring the cache hit percentage. If
the percentage improves, the setting can be increased again until no improvement in
performance is seen.
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