PAGEIOLATCH_SH: Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Shared mode. PAGEIOLATCH_SH waits is very brief as they are only held on a page during IO operations.
You can also identify I/O bottlenecks by examining the latch waits. These latch waits account for the physical I/O waits when a page is accessed for reading or writing and the page is not available in the buffer pool. When the page is not found in the buffer pool, an asynchronous I/O is posted and then the status of the I/O is checked. If I/O has already completed, the worker proceeds normally. Otherwise, it waits on PAGEIOLATCH_EX or PAGEIOLATCH_SH, depending upon the type of request. The following DMV query can be used to find I/O latch wait statistics.
Select wait_type,
waiting_tasks_count,
wait_time_ms
from sys.dm_os_wait_stats
where wait_type like 'PAGEIOLATCH%'
order by wait_type
More detail information on performance probblems in SQL Server 2005, please navigate to the following article.
Troubleshooting Performance Problems in SQL Server 2005
http://www.microsoft.com/technet/prodtechnol/sql/2005/tsprfprb.mspx