Published under Category : Hard Disk Drives

All about the Seagate 2X18 Mach.2 drive with dual actuators

It was almost a year ago when Seagate unveiled the specifications for the Mach.2 drive and planned to launch only SAS drives that would present themselves to the host as 2 LUNs. Since SATA 's specifications do not allow for multiple LUNs, there was no plan to bring a SATA drive to market.

A year later they have now launched dual actuator drives with both SATA and SAS interfaces. With SAS the drive still presents itself as 2 LUNs, but with SATA the internals are managed by the drive and the SATA drive presents itself to the host as a single 16/18TB drive.

Before we look at the drive specifications, a little background on the benefits of Dual Actuator (or in some years Multi Actuators) drives.

As HDD capacities increase and transfer rates stagnate, dual actuator drives solve this problem.

HDD recording technologies such as energy- assisted magnetic recording have given us larger HDDs - at the time of writing, 24 TB and very soon there will be 28-30 TB HDDs.

However, the recording breakthroughs have had no impact on transfer rates. The end result: we have larger hard drives that are just as slow as their smaller counterparts. To avoid this bottleneck, the transfer rate must be increased. By using 2 independent actuators and parallel read/write, transfer rates could theoretically be doubled - just like a RAID 0 setup. This is what the dual actuator drive tries to achieve.

SAS is represented as 2 LUNS, SATA as a single drive

Seagate's literature talks about 2 LUNs for the SAS drive, so your host will see 2 logical units, but SATA cannot have multiple LUNS, so SATA works similarly to RAID0, where a single block device is represented to OS.

Part numbers and encryption options

For 2X18, There are 2 capacities listed on the datasheet - 16TB and 18TB. SATA has only 1 single variant, Standard FastFormat. It is shipped as 512e but can be formatted to 4Kn. SAS will have 2 variants - the standard model and the SED model , both with FastFormat. Currently there are no SED-FIPS models.

Part Number Capacity Platform Interface Encryption Format
ST18000NM0272 18 TB 2X18 SAS None FastFormat
ST18000NM0012 18TB 2X18 SAS SED FastFormat
ST18000NM0092 18TB 2X18 SATA None FastFormat
ST16000NM0002 16TB 2X18 SAS none FastFormat
ST16000NM0012 16TB 2X18 SAS SED FastFormat
ST16000NM0092 16TB 2X18 SATA None FastFormat

Almost Double the transfer rates, double the random read IOPS

let’s compare X18 ( single Actuator ) drive performance with 2X18 ( Dual Actuator drive).

  X18 Single Actuator 2X18 Dual Actuator
Max Suistained Transfer rate OD MB/s 270 545-554
Random Read 4K QD16 IOPS 170 304
Random Write 4K QD16 IOPS 550 560
Average Latency (ms) 4.16 4.16
  • Max Suistained xfr rate has almost doubled. SATA has a marginally lower XFR rate then SAS.
  • Random Read IOPS have also almost doubled
  • Random write IOPS are almost the same. Most probable reason is that both the X18 and 2X18 have 256MB cache. Write requests are writtent to the cache first and reported to be written.
  • Average latency is also the same for both. Both have the same 7200RPM so the rotational latency is the same for entire Exos series.

Going forward as the hard drive capacities increase,vendors will have to find ways to increase the transfer rates. Its just a matter of time before other vendors come up with multi actuator drives also as nobody wants bigger, slower drives.


Akash @ Wed, Dec 14, 22

In reply to @boe.

A few years ago, before power assisted recording was available for HDDs, there was all sorts of speculation about how SSDs would kill off HDDs. In every presentation we saw the graph of SSD prices plummeting and VS HDD prices stable and the point where they would meet – the point where SSDs would be as cheap as an HDD and HDDs would be dead

But then energy-assisted recording – HAMR and MAMR – made a much larger HDD possible than what could be – 20TB, 22TB and 30TB (Yup 30TB would hit the market in Q2 2023) – there is no way SSDs could even come close to HDD pricing in these large capacity. So the scenario today is that SSDs would overtake HDDs in the smaller capacities (smaller than 4TB) and HDD manufacturers would no longer be interested anyways in those capacities.
At larger storage capacities – For us as system integrators, it’s never a question of SSD or HDD, but rather the use of SSD and HDD, either through tiering, caching or separate volumes. Dual actuators are going to make the HDDs tranfer rates higher, for 18TB+ Capcacity you need higher rates.

boe @ Thu, Dec 01, 22

I was hoping by now we’d see Samsung 16 TB SATA SSDs on the market in the $500 range. Hopefully 32TB in the $700 range a couple of years from now. I really thought Samsung was going to make a lot more progress than they have. Oh well my loss. I wanted to build about a 160TB RAID 5 out of SATAs in the next couple of years. I’m guessing now that that is another 7 years away due to price and technology.

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

FREE Delivery in UAE

Including Dubai, Abu Dhabi and Sharjah

NAS Experts

QNAP , Synology Top Sub Distributor and Service Partners in UAE

TOP Integrator

Second time Winner of GEC Awards in Data Storage Category UAE

Honest and Credible

4.8+ Star Google rating. Thousands of satisfied customers in UAE