Is reading from remote networked memory mapped file or device block faster than reading from Local 7200rpm HDDs?

Question

Or rather how does remote RAM compare against local Disk access? If the answer is "it depends", what are the conditions? Data access patterns, ratio of read-to-writes, distance etc.

Finally, what if the local disks are NetApp filers?

Thanks.

Answer 1

It is as always a question of latency versus bandwidth. The access time to remote memory will be on the order of microseconds for gigabit networking, 100s of nanoseconds for InfiniBand and 10 GigE compared with milliseconds for local disks (example Seagate ST3250318AS - 4.1ms). As soon as the disk has hit a contiguous block it's transfer rate will exceed gigabit networking which is why local disk is predominantly considered faster.