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Seagate 20TB IronWolf Pro Review

Just when you thought NAS-specific hard disks couldn’t get any larger, along comes Seagate and bumps its IronWolf Pro up to a massive 20TB capacity. Seagate has always been at the forefront of hard disk design and innovation and this new model puts it alongside Western Digital’s 20TB Red Pro NAS and ahead of Toshiba which, although it has announced a 20TB MG10 model, has yet to start shipping it.

As a member of the IronWolf Pro series, the 20TB drive offers a range of advanced technologies that allows it to safely operate in rack-dense environments and NAS appliances with up to 24 bays. Storage-hungry businesses will approve of this as it means they can push raw capacity of a single NAS appliance up to a gigantic 480TB.

Hard disk features

Seagate IronWolf Pro 20TB NAS DriveThe 20TB IronWolf Pro targets a wide range of business storage applications including commercial and enterprise NAS, video production, shared storage, workstations and servers. It introduces some new design features as whereas the 18TB IronWolf Pro drive employs 9 platters and 18 heads, the 20TB model increases these to 10 platters and 20 heads.

The 20TB drive has a 7.2K spindle speed and comes with a 256MB DRAM cache – the same as the 18TB version – and, surprisingly, continues to use conventional magnetic recording (CMR) technology. In our world exclusive review of the 18TB IronWolf Pro, we had expected this model would be the last to use CMR technology as Seagate was planning to shift production to the higher density shingled magnetic recording (SMR) for its next generation of high-capacity hard disks.

The drive offers a Mean Time Between Failures (MTBF) rating of 1.2M hours and workload rating of 300TB/year – the same as its other IronWolf Pro stablemates. These are designed to cater for businesses shifting large amounts of data between their users and the appliance on a regular basis but if these numbers aren’t high enough for you, the enterprise-class 20TB Exos X20 boosts them to 2.5M hours and 550TB/year.

Seagate has squeezed out a little extra performance as a single 20TB drive has a maximum sustained transfer rate of 285MB/sec making it the fastest IronWolf drive currently available. This is also slightly higher than WD’s Red Pro which claims a sustained transfer rate of 268MB/sec.

AgileArray technology

A feature common across all the IronWolf and IronWolf Pro family is Seagate’s AgileArray technology which increases reliability in multi-drive NAS appliances. It’s a smart combination of firmware, hardware and software features that aim to reduce vibration, accelerate error recovery and control power consumption.

Unlike Seagate’s PC hard disks which are designed to operate as single devices, the firmware and caching algorithms in the IronWolf Pro drives are specifically optimized for multi-drive RAID arrays. A RAID volume will have data distributed across multiple drives and these enhancements aim to accelerate performance when accessing large files such as videos.

Unrecoverable errors can be a major issue in RAID arrays as these can take minutes to resolve as the controller tries to read the data from each drive in turn. Seagate’s Error Recovery Control (ERC) speeds up this process with a shorter default recovery timer that’s also adjustable.

Rotational Vibration (RV) Sensors

Placing multiple drives in close proximity in a RAID array will produce unwanted vibration that has the potential to accelerate hardware failures and errors. Seagate’s RV sensors detect excessive vibrations and protect the drive and heads against any potential long-term damage, thus increasing their lifespan.

There’s more as Seagate’s AccuTrac comprises improved servos and actuators that react quicker to extreme vibration. All IronWolf drives also use a dual-plane design which further reduces vibration and noise from the drive’s motor.

Health monitoring and recovery services

A feature business NAS users will approve of is Seagate’s IHM (IronWolf Health Management) as it allows them to keep a close eye on drive performance and will alert them to impending failures. This is an advanced feature that can be used to test IronWolf Pro drives regularly, view logs of the results, run daily read/write statistics analysis tasks and load historical graphs of drive usage over time.

IHM support is implemented by NAS manufacturers in their OSes and is generally accessed from the respective storage management app. Rest assured all the major NAS vendors support IHM and include Qnap, Synology and Qsan.

The IronWolf Pro drives are a great choice for businesses running mission-critical apps as they come with a generous 5-year warranty as standard and include a 3-year subscription to Seagate’s Rescue Data Recovery Service. Once the drives have been registered, this enables immediate access to Seagate’s data recovery gurus who will assist with on-site data restoration in the event of a failure.

Lab testing environment

The 20TB IronWolf Pro is primarily designed for use in NAS appliances so there’s no point in testing a single drive in a PC as this isn’t an appropriate usage scenario. For real-world testing, we used Qnap’s TVS-882BR – one of its high-end 8-bay SMB models that’s equipped with a 3.6GHz quad-core Intel Core i7-7700 CPU and 32GB of DDR4 memory.

To ensure the test drives weren’t hindered by OS overheads, we installed the QTS system software on a dedicated mirror comprising two enterprise-class 1.92TB Micron 5200 Max SATA SSDs. We then fitted two 20TB Seagate IronWolf Pro drives and used the QTS Storage Manager app to create an 18TB RAID1 mirrored storage pool.

Testing Setup for our Seagate IronWolf Pro 20TB Review

Qnap TVS-882BR + ATTO Celerity FC-164P HBA with quad 16Gbps FC ports + Dell PowerEdge T640

To push the drives as hard as possible, we took advantage of the fact that Qnap supports Fibre Channel and installed an ATTO Celerity FC-164P HBA with quad 16Gbps FC ports in the appliance. For our test host, we used the lab’s Dell PowerEdge T640 tower server with dual 2.1GHz 22-core Xeon Scalable Gold 6152 CPUs, 384GB of DDR4 plus an ATTO Celerity FC-164P HBA and running Windows Server 2019.

We created a dedicated 1TB FC LUN on the test drive array and mapped it to the host server over a dual-port 32Gbps MPIO FC connection. Tests were conducted with Iometer configured with 256KB transfer request sizes for testing maximum sequential and random read/write rates and 4KB request sizes to measure IOPS throughput.

Performance results and analysis

Overall, the 20TB IronWolf Pro delivered excellent performance in our real world tests with sequential read and write rates measured at a steady 3,152MB/sec and 3,150MB/sec. Moving over to random operations saw read speeds settle comfortably at 3,152MB/sec while write operations dropped to 89MB/sec although our 100% random write test is a worst-case scenario as few businesses will have these kinds of workloads.

I/O throughput was equally good as changing Iometer to 4K blocks saw high sequential read and write rates of 650,000 IOPS and 526,600 IOPS. For random reads operations, the array held steady at an impressive 614,250 IOPS while write operations saw an expected drop down to 3,175 IOPS.


SMBs and enterprises that want to maximize the storage potential of their NAS appliances will find Seagate’s 20TB IronWolf Pro an irresistible choice. As one of the highest capacity and fastest NAS-specific hard disks on the market, it offers an impressive range of technology features designed to ensure reliable, 24/7 operations.

Clearly geared up for heavy workloads in large NAS appliances of up to 24 bays, the 20TB IronWolf Pro delivered an impressive performance in our real world tests. Costing $575, it is very competitively priced and offers peace of mind with a generous 5-year warranty and full access to Seagate’s data recovery specialists.

9.3Expert Score
Seagate’s 20TB IronWolf Pro is an Irresistible Choice

Clearly geared up for heavy workloads in large NAS appliances of up to 24 bays, the 20TB IronWolf Pro delivered an impressive performance in our real world tests. Costing $575, it is very competitively priced and offers peace of mind with a generous 5-year warranty and full access to Seagate’s data recovery specialists.

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