How to Choose a Hard Drive -

How to Choose a Hard Drive


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

What is important in the evaluation of the drives is in two areas. First, performance, which includes streaming I/O performance and seek and latency time and of course reliability, and second, support for things coming like 4K sectors, encryption and end to end data protection.

You can see from the table that, with the publically available information that I could find, Toshiba and WD lack information in a number of areas that should be evaluated. So that leaves HGST and Seagate as the only vendors that really can be evaluated and there are of course tradeoffs between these two vendors. But Seagate has high MTBF and better performance for both seek and latency and for streaming I/O.

Enterprise SSDs

In looking at enterprise SAS attached SSDs, a few interesting things are apparent when you start to look at the data. All numbers were normalized from the vendor provided data for easy comparison.

1. For all vendors the difference in performance for read and write is significant. Write was only X % of read (HGST 56%, Seagate 67%, and Toshiba 42%).

2. Toshiba had a significant performance reduction for read if using a drive that supported encryption.

3. Hard error rate reliability is the same as enterprise 2.5 inch drives for Seagate, for HGST it was 10x better than their 2.5 inch drive, and Toshiba provided no data.

4. The endurance is listed and is a big issue for the drives. See below for a review of the information provided.

how to chose a hard drive

*HGST write value is 231 MB/sec for 5 years

**HGST assumes 4 KiB aligned I/O requests

***Seagate Warranty terms will vary based on type of warranty chosen: “Managed Life” or “Limited Warranty with Media Usage.” Consult the Seagate sales representative for warranty terms and conditions

****Sustainable 4KB Random combined IOPS for 5 year Endurance (65%/35% R/W, 70% Duty Cycle)

*****Note Toshiba numbers are higher (~18%) for the non-encrypted drive read rate.

#Random reads and/or writes for 12.0Gbit/s interface speed by dual port.

##Toshiba warranty is 5 years or the max TBW (total bytes written) per model capacity whichever occurs first.

##Toshiba values are based on write rate of 92 MB/sec for 5 years. Definition and conditions of TBW (Terabytes Written) are based on JEDEC standard; JESD218A, February 2011, and defined for the service life.

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




Hard Drive Endurance

The Seagate formula above was confusing to me. So I have translated into something that I found more understandable.

how to chose a hard drive

Each of the vendors state that you need to stay within their write budget to meet the support requirements for a 5 year warranty. The below table shows the MiB/sec that each of the vendors supports to meet this requirements. I have included the percentage of total bandwidth as a function of the total write bandwidth of the drive to meet the 5 year write budget support requirement.

how to chose a hard drive

I believe that these numbers are pretty good. With the HGST drive you can write on average 220.2999 MiB/sec to the drive 24x7x365x5 and meet the support requirement.

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