How to Choose a Hard Drive: Page 2 -

How to Choose a Hard Drive - Page 2


How Real-World Numbers Make the Case for SSDs in the Data Center

Toshiba did not provide a great deal of information on their drive so it is hard to determine how it really compares in many areas. Hitachi clearly has the highest MTBF by over 600,000 hours. This is pretty amazing as back in 2005 enterprise fibre channel drives had about that number of hours as their MTBF, if I remember correctly. That is a big change over the last 9 years.

On the other hand the hard error rate of 1 bit in 10E15 bit read has not changed much over the same period of time. The HGST drive is a bit louder than the competition and uses a bit more power. So my recommendation would have to be between Seagate and HGST, and I would stay away from the WD drive for enterprise applications given the 180 TB workload limitation.

In Closing In comparing these two drive types it is very clear to me that consumer drives should not ever be used in an enterprise application. If they are, then shame on the system architect and buyers because the drive vendors are clearly specifying the usage environments and criteria for usage, such as the amount of data that can be written. Though the temperature ranges for both types drives is about the same, they are some clear differences. Consumer drives use SATA connectivity only, not SAS which has:

1. Higher reliability in the channel for ECC, which significantly reduces the potential for silent data corruption by many orders of magnitude.

2. Coming support for 12 Gb/sec interfaces, which are available today in some high end drives and will never be available for consumer drives as SATA’s future is 8 Gb/sec.

3. On drive error recovery is much more robust with SAS as compared with SATA.

4. SATA does not support the ANSI T10 end-to-end data protection model with validation of a CRC and LBA at the disk drive for high reliability.

Last but certainly not least is the desire in the enterprise for encryption of the whole disk drive. HGST and Seagate have a large number of details on encryption and how it works and that it has no impact on performance. Being in an enterprise environment, especially in a cloud environment or backup environment, means that the data is out of your data center being managed by someone else.

Now many of these services do provide their own encryption, but some do not. Having full disk encryption from my point of view is a must have and another major reason, due to reliability, that consumer drives should never be used for enterprise applications. Because if a hard drive gets removed from the environment it is unreadable.

How to Choose a Hard Drive: The Enterprise

Now, I’ll focus on choosing a hard drive for the enterprise. I’ll look at four enterprise SAS 15K (10K for WD as I wanted to include them) and three enterprise SSDs. The data presented here was collected from each of the vendor’s web sites January 31, 2014.

As a reminder, as mentioned earlier in article, Seagate had the best documentation, followed closely by HGTS, while Toshiba and WD were very far behind. This was true for both hard drives and SSDs. The following hard drives were evaluated.

• Toshiba-Enterprise 2.5 inch 15K RPM and enterprise SSD

• HGTS-Enterprise 2.5 inch 15K RPM and enterprise SSD

• WD-Enterprise 2.5 inch 10K RPM (No SSDs were listed)

• Seagate-Enterprise 2.5 inch 15K RPM and enterprise SSD

Both of the hard drive types chosen are enterprise drives with the highest reliability and performance provided by the vendor for SAS attached drives. I did not look at SSDs with PCIe connectivity even though some of the vendors listed manufacture them.

Enterprise 2.5 inch drives

Here is the information on the 2.5 inch 15K hard drives, and the enterprise10K for WD. Also note that HGST, Seagate and Toshiba all make enterprise 10K drives with similar density to WD. As you can see, this table is a bit different than the SATA/SAS nearline table from earlier in this article, as there are a number of new things that should be considered when evaluating these types of hard drives.

how to chose a hard drive

* Ambient Temperature 5°C to 55ºC, Relative humidity 5 to 90%, non-condensing Maximum wet bulb temperature 29.4ºC, non-condensing Maximum surface temperature gradient 20ºC/hour, Altitude -305 to 3,048 m.

**Only average power is listed.

Here is the location of some of the documentation for each drive:





Hard Drive Key Characteristics

With one exception for the HGST 4 TB drive, each of the other 3 enterprise 2.5 inch drives have a higher MTBF for the same vendor than the 4 TB drives reviewed earlier.

The lack of information from both Toshiba and WD I find annoying. I guess their belief is that this data does not need to be public as the public generally is not buying these type of drives. But this attitude doesn’t help them, and neither Seagate nor HGST think this way. Here are my thoughts.

The PC industry is being driven for the home user by the gaming community. If we can all agree on that then consider that SAS now runs at 12 Gbit/sec while SATA is stuck at 6 Gbit/sec, at least for 2014, from what is being said in the industry. Even when SATA gets to 8 Gbit/sec SAS will be nearing the availability of 16 Gbit/sec.

The need for speed in the gaming workload, I think will drive many from SATA to SAS. What is missing is SAS-based motherboards. I checked a few motherboard vendors and at least today, none of them has SAS motherboards for the gamer community.

The vendors all seem to do have them for their CAD workstations, but 12 Gbit/sec is somewhat new from the ~4Q13 time period for the mass market release, and I suspect that by mid-year we are going to see movement to sometime by mid-summer. The costs of 12 Gbit SAS support is not going to be much in the overall cost of a system. Of course if Intel would support SAS then it becomes a moot point.

So you might ask: why talk about SAS at all? The reason is that if SAS is available, these high performance drives might make it into home PCs and storage appliances for people with higher end needs. This would, I would hope, kind of force Toshiba and WD to provide some reasonably complete documentation on their products.

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