Troubleshooting a SQL Server with OS Disk and Network Based issues/Miscellaneous Counters
The areas we need to look at are Physical Disks, Network Interface etc
Check the counters like
Physical Disk- Avg. Disk Sec/Read < 8ms(Not Applicable to SAN since it has its own Cache and processor)
Physical Disk Avg. Disk sec/Write < 8ms (non cached) < 1ms (cached)
Network Interface-Bytes Total/sec