SSD Alignment: Why you should quickly benchmark every SSD
Modern operating systems work well when installing a new SSD. Years ago this was not true since SSDs were new and exotic. As 2014 comes to a close, most modern operating systems are able to quickly setup SSDs with the correct alignment/ offset for them to work at peak performance. Having the correct alignment/ offset when setting up a SSD was previously a significant issue. Computers and operating systems, for years, have used rotating storage as their default medium. When the hard drive manufacturers moved to larger disks, necessitating 4K block sizes over 512B block sizes we saw some of those assumptions being tested. While having a misaligned hard drive can cause performance issues, solid state drives can suffer other drawbacks. One example of this is that improper alignment/ offset can cause excess writes to the underlying NAND, thereby decreasing performance and effective write endurance.
As part of our SAS SSD quick benchmarking we recently looked at the Seagate 1200 400GB SAS SSD. In the test bed we were, of course, testing the 200GB parts. We picked one of the Seagate 200GB SAS SSDs and saw this graph after conditioning but upon the AS SSD benchmark run on our 6gbps SAS2 controller under Windows Server 2012 R2:
Clearly something as amiss. Luckily we had the second Seagate 1200 200GB drive on the same controller and saw much higher performance. One can see in the screenshot that the 4K-64Thrd numbers look about right but the sequential numbers are significantly off. We found that the drive alignment/ offset was a big factor in this performance difference.
The lesson here is that it does pay to spend a few minutes running fast benchmarks on new drives. Long sessions like we are running with iometer on these drives (and as we previewed in our Intel S3700 100GB v. 710 100GB quick benchmarks recently) are usually not necessary to check that drives are working properly.
The fix was simple, we deleted partitions and re-initialized drives. The net impact is that the 200GB Seagate 1200 SAS SSDs were working properly again and ready for single drive and RAID testing once the offset was fixed.