Are 15K drives more efficient than 10K?

In the course of discussions with the client about the configuration and size of the storage, I went down to a fairly low level of detail. To my surprise, it turned out that 15,000 rpm disks do not have to be faster than 10K disks !!!

It is assumed that the performance of various types of disk drives should be estimated as follows:

RPM	IOPS
SSD	6000
15K	175
10K	125
7.2K	75
5.4K	50

For more information on disk performance, please read the well-documented one Wikipedia article. During empirical tests conducted in our company, the performance of arrays with 15K disks exceeded the performance of 10K disks by up to 30% (HP EVA4400 450GB 10K and 15k disks, EVA6000 300 GB 10K and 15K disks).

In order to choose the best performance and cost-effective solution for our client, 2 variants of the storage configuration installed in the DL380G8 25SFF server were compared:

• 16 x 300GB 15K 2.5 ″,
• 16 x 600GB 10K 2.5.

To learn more about the performance of these drives, I had to use the datasheets of similar Seagate drives, because HP does not publish such detailed data on the drives used in their solutions.

In general, the performance of a disk array depends on many factors:

• disk performance (interface 6/12 Gbps, disk cache size - is 16MB, rotational speed),
• type of disk interface and its performance (in this case SAS 6Gbps),
• matrix driver performance,
• performance of the interface connecting the computer with the array (in this case PCIe),
• Array driver cache size (SmartArray has a 2GB cache),
• disk occupancy (the speed of continuous disk reading depends on the track number, external tracks are faster as shown in the table below),
• type of load on the part of the application (e.g. databases generate a random load, with a predominance of reads, with a small block of data, and therefore often read with only the cache).

As you can see, there are many factors in a disk system that can affect performance and create bottlenecks. The table below provides links to datasheets for Seagate 10,000 and 15,000 RPM server drives. The parameters that by definition determine the performance of these 2 types of disks are the sustained rate and the average access time. However, it can be seen that for both models these differences are practically insignificant:

Disk type	ANDContinuous transfer	ANDAverage access time
Savvio® 10K. 6	204 up to 125 MB / s	2.9 ms (average)
Savvio® 15K. 3	202 up to 151 MB / s	2.6 / 3.1 ms (read / write)

It is a big surprise that in the case of both models of Seagate drives, their rotational speed has such a small impact on the average access time, depending on the delay associated with waiting for the availability of the appropriate sector on the rotating disk. Also, the value of continuous data transfer from and to disk has similar values.

The above-mentioned considerations show that the performance of a disk channel based on 10K disks does not have to be lower than that built on high-speed 15K disks, especially in the context of the existence of various types of bottlenecks in the solution being built. An additional factor worth considering is the ratio of the price and capacity of the disks used - the models described in the table above cost PLN 1,086 and PLN 1,715, respectively (according to ceneo.pl). gross. The much cheaper 10K drive at a lower price offers 2 times more capacity.

Not always what is more expensive has to be better: o)

A detailed description of the contemplated configuration is provided below.

P / N list in configuration:

- 704558-421 HP DL380p Gen8 E5-2650v2 25SFF EU Svr - 1 piece,
- 708641-B21 HP 16GB 2Rx4 PC3-14900R-13 Kit - 2 pieces,
- 652611-B21 HP 300GB 6G SAS 15K 2.5in SC ENT HDD - 16 pcs.

Detailed specification of the server configuration:

- 2 x Intel® Xeon® E5-2650 v2 processor (2.6GHz / 8-core / 20MB / 8.0GT-s QPI / 95W, DDR3-1866, HT, Turbo2- 4/4/4/4/5/6 / 7/8),
- cache memory: 20MB (1x20MB) Level 3,
- 64GB (2x16GB) PC3-14900R (DDR3-1866) Registered DIMMs,
- HP Smart Array P420i / 2GB driver with FBWC (RAID 0/1/1 + 0/5/5 + 0/6/6 + 0),
- HP FlexFabric 10Gb 2-port 533FLR-T Adapter network card,
- internal storage: 25 SFF SAS / SATA HDD Bays; includes 23 SFF hard drive blanks,
- 6 x PCI Express slot,
- installed disks: 8 x 300GB 15K SAS disk,
- power supply: 2 x HP 750W CS Platinum Plus Hot Plug Power Supply (94% Efficient),
- cooling: 6 fans (N + 1 redundancy standard),
- management: HP iLO Management Engine (standard) - remote console, virtual drive etc.,
- housing: Rack (2U), HP Ball Bearing Rail Kit without Cable Management Arm,
- Warranty: 3-years parts, 3-years service, 3-years on-site, next-business-day.