SSHDs: Hitting the sweet spot on balance of storage space and performance

By Team Digit | Updated 21 May 2014
SSHDs: Hitting the sweet spot on balance of storage space and performance
  • Promotional Feature: We take a closer look at the mechanics of caching in SSHDs and get an idea as to how cost-effective they are

In the previous article we explained what the whole concept was behind the new storage innovation that has been dubbed the SSHD (Solid State Hybrid Drive). We’ll now be going into the drive in further detail this time and all doubts about the drive and the underlying technology should be hopefully erased after you’ve gone through this one.

A little about SSD caching
When SSDs started coming into the market they were pretty expensive and though they are more affordable now the price/GB ratio is still higher than normal hard drives. Around the same time manufacturers started getting innovative with SSDs and we soon saw the introduction of SSD caching. The feature worked like this, a separate software was installed to monitor which applications are more commonly used on your computer and depending on the frequency of usage that particular software would get cached onto the SSD. So the next time the software would be loaded onto the system memory from the SSD instead of the hard drive. The files on the hard drive would still be there so you need not worry about losing those. Simply put, your commonly used applications would load much faster.



When you look at the technology as a whole, there was the need for a hard drive, a SSD and a specialised driver to monitor the commonly used software that needed to be cached. On Seagate’s SSHD, all of this is done on just one hardware – the SSHD. Essentially, it’s a simple implementation of the previous generation technology except it’s easier to work with. There are no special drivers or software needed. The controller exists on the SSHD and it monitors the frequently accessed files so that they can be cached.

The SSHD models are available in different form factors and come in varying capacities. The maximum of which has 4TB of storage capacity. These drives only sport a minor price premium over regular drives but performance wise they score much better. This has led the SSHD being purported as a balance between performance and storage. We’ll be looking at the numbers in further detail over the next few articles and it should be more than evident by then

So how good is it?
Let’s consider a few hard drives and compare them. We’ll take a few desktop Seagate hard drives and then a few Seagate SSHDs. A simple application start-up and operating system boot-up test will be run. The deal with SSHDs are that the more frequently you run a particular application the faster it will load the next time. This is because the SSHD detects that it is a frequently used application and will cache the frequently used files on the eight gigabytes of flash memory that is available on the SSHD. The numbers are quite surprising.

1. Operating system startup time

On the very first run the OS boots up at roughly the same time on both types of hard drives. The time comes down to 49 seconds on the SSHD and 50 seconds on the HDD. Now as we reboot a couple of time the time slowly starts dropping on the SSHD while on the HDD it remains the same. Towards the end the time comes down to 40 seconds. Over the course of the test we can see that the cumulative performance increase over eight iterations amounts to 20%. In the constantly evolving realm of computer hardware such an increment is indeed tremendous.

2. Application load up time

This test is similar to the one above wherein a certain application sets are selected (multiple Adobe software) and then a batch file is created where these applications are opened at the exact moment. So a successful test run is when all individual applications have opened up. On the very first run we do see a minor difference of 6 seconds where the SSHD is ahead of the HDD. But as we progress through the different runs the load time difference widens to such an extent that one would wonder that there might be an SSD in the heart of the system. On the final run the load time was 15 seconds. Which is a 52% increment in load time.

3. Spin up time
In all due ridiculousness of the graph we won’t be putting it up in this segment. A hard drive is a mechanical device which means when it starts up for the first time during a boot sequence the platters start spinning and they have to reach a bare minimum RPM before the hard drive head (the object that reads and writes data) can move in to access data. This is called the spin-up time. On a hard drive this time varies by a huge margin, 5400 RPM drives are ready earlier than 7200 RPM drives and subsequently 10,000 RPM drives come online. But SSHDs access the OS files from the flash memory rather than the platter. So these get ready at the exact time as SSDs do. Which is why the SSHDs are ready in about 0.5 seconds while HDDs take anywhere from 4 to 7 seconds.

3. Cost per gigabyte


If you’d recall then we did mention that SSHDs come at a price premium. Here we’re looking at two models. One is a normal laptop hard drive (ST500LT012) and the other is an SSHD (ST500LM000). The hard drive costs Rs. 3,800 while the SSHD costs Rs. 5,800. This brings the cost per gigabyte rate to 7.8 for the HDD and 11.6 for the SSHD. So the price premium that you are paying is so negligible in the face of the huge performance boost that you receive. If you consider SSDs then they cost roughly Rs. 22,499 which gives you Rs. 45 per gigabyte.

Final word
The SSHD performs better than hard drives on an average, they boot up faster than hard drives. And finally it is much economical to invest in an SSHD since the cost per gigabyte is a lot lesser than SSDs and is barely above that of HDDs. We see that the SSHD has managed to achieve a balance between SSDs and HDDS and they are a better investment now. Eight gigabytes of flash memory may not seem to be a lot but the performance figures tell another story.

Team Digit
All of us are better than one of us.

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