X-bit labs

SSD, i-RAM and Traditional Hard Disk Drives (page 4)

Category: Storage

by Aleksey Meyev

[ 04/23/2008 | 08:05 PM ]

Disk Response Time

In this test IOMeter is sending a stream of requests to read and write 512-byte data blocks with a request queue of 1 for 10 minutes. The total number of requests processed by the HDD is over 60 thousand, so we get a sustained response time that doesn’t depend on the HDD’s buffer size.

Based on SDRAM, the i-RAM is the only device that can beat the SSDs in terms of read access time. As for HDDs, even Fujitsu’s drive with a SAS interface and a spindle rotation speed of 15,000rpm (it is the rotation speed that largely determines the read access time of a HDD; the areal density has a smaller effect) proves to be 30 times as slow as the SSDs. The more widespread 7200rpm HDDs are even slower.

The SSDs fall behind in terms of write access time, though. The HDDs’ access time is about two times better than at reading because write requests are first entered into the cache memory and then, in optimized order, written to the platters. An SSD has to write directly to memory and flash memory has never had a high write speed. By the way, comparing SSDs with modern memory cards and USB flash drives, we can see that they use fast chips, yet not the fastest available. Perhaps some fast cache memory would help organize simultaneous writing into different flash modules, but this is not implemented yet.

The i-RAM is ahead of the other devices, enjoying a huge lead. Writing and reading into SDRAM modules takes almost no time at all if compared with the drives.