Published under Category : Hard Disk Drives

Seagate mach.2 is actually 2 drives in a single drive

Seagate mach.2 drive double up the transfer performance, thanks to 2 read/write heads.

Hard drive capacities have been increasing and will continue to do so thanks to Energy assisted Recordings.  Within last year the highest capacity has jumped from 14TB to 18TB. 

But the transfer rates and IOPS ( performance) have not increased in the same proportion.  The Result: A bigger capacity drive with the same transfer rate as a low capacity drive.  It also means that the average performance per TB falls in the same proportion as the capacity increases. 

So today, an array of 2 x 8TB Exos striping for example would outperform a 16TB single Exos drive. Why not increase the transfer rates then? Because it's not easy. Traditional measures like increasing RPM, caching and short stroking, etc have either reached their higher limit or come with a higher cost/ capacity lost.

So the only way to increase performance is to emulate the RAID array I mentioned earlier - 2 independent drives with independent Read/write heads ( called Actuators), working together to combine the transfer rates and this is what Seagate mach.2 tries to achieve sans the RAID mechanism 

Dual Actuators - Double the performance ( with Load balancing)

So you deploy 2 actuators and make sure they are both share the workload, and you have a combined performance.  Since there are 2  independent actuators taking care of one-half of the drive's media, these are actually 2 independent drives. Now, if your application/OS can achieve parallelism ( writing in stripes like RAID 0 for example), you will have double the performance.  And that's where the trick is- making sure that workload is divided across both halves. 

Application needs to be aware of dual drives 

With two independent actuators - there are 2 data paths.  While the form factor and physical connection is that of a single drive - these are actually 2 different drives in a drive. 

So how do you present these 2 drives to the OS?  As 2 entities, leaving load balance to the OS, or as a single drive with in-drive load balancing mechanism 

With Seagate SAS drives, it's the former case. Each drive is presented to the OS as a separate LUN, and your application needs to be aware that these 2 independent LUNs belong to the same physical drive, and it's a single port SAS.   So far there is no implementation on SATA but if that happens, it would probably be around the same lines - presenting a single drive with 2 partitions to the host, leaving it up to the host to do workload distribution and redundancy optimization. 

Not Double the Power Consumption 

While intuitively it may seem like 2 actuators will double the power consumption it's not the case actually. There are many common components that don't double up the consumption.  The average Power consumption of Dual Actuator drives is about 20% higher than a single actuator drive.  But the performance is double, so if you consider two single actuator drives (offering the same capacity and performance as dual actuator), the dual actuator drive actually has lower power consumption. 

Seagate has mach.2 How about other vendors

Given that the only option to boost performance with the current technology is to increase the number of actuators, other vendors will have to work on this too. 


About Author : Akash Jain

I have worked in Data Storage Industry since 1998. I loves Technology and write often about NAS, Hard drives, Tapes and Flash technologies

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