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Seagate Exos Drives: Reading an ST Part Number
GTR Supply buys and sells Seagate Exos drives by the lot, from a pallet of array pulls up to the contents of a storage refresh, and this page shows you how to read an ST part number so a list means something. Seagate encodes a remarkable amount into that number: the capacity, the drive family, the interface and the sector format all sit inside it. That last one is the reason this page exists. Two Exos drives of the same capacity, from the same family, can be entirely different parts because one is 512e and the other is 4Kn, and mixing those inside an array is the most common expensive mistake in drive lots. Every part number and family name on this page is identification help for the reader, never a stock listing. Send the ST numbers with counts and we will tell you where we stand.
How to identify it
Work out what you have.
Where the identifying number physically sits, how to read each field in it, and what it tells a buyer. Useful whether or not you ever trade anything with us.
Reading an ST part number
Seagate drive part numbers begin ST and then read in three parts.
First the capacity, in gigabytes, written straight into the number. ST16000 is a 16TB drive, ST8000 is 8TB and ST600 is a 600GB drive. That is the easiest field on any drive label in the industry.
Then two letters that identify the drive family and the market it was built for. NM is the 3.5 inch nearline enterprise line, which is where Exos lives, and NX is its 2.5 inch equivalent. MM and MP are the 2.5 inch mission critical drives, the ten and fifteen thousand revolution parts. Outside enterprise, VN is the network attached storage line, DM is the desktop line and VX is the surveillance line, and all three turn up in mixed pallets.
Then a short trailing group that identifies the exact variant: the interface, the sector format, the cache size and whether the drive has self encryption or secure erase features. Those trailing characters are where two drives with identical capacity and family become different parts, so never truncate a part number when you write a list.
512e against 4Kn, and the array trap
Every hard drive has a physical sector size and a logical one it reports to the host, and the combination is written into the part number rather than printed as a plain description.
A 512n drive uses 512 byte sectors physically and logically, and is now only found on older parts. A 512e drive uses 4096 byte physical sectors and reports 512 byte logical ones, which is what most drives in circulation are. A 4Kn drive uses 4096 bytes physically and reports 4096 bytes logically.
The trap is that a storage array or pool built on one logical block size will not accept a drive using the other as a replacement. The drive is healthy, the capacity matches, and the rebuild refuses to start or the controller rejects the drive outright. Many controllers will not mix the two inside one volume group at all.
One genuinely useful difference between interfaces: SAS drives can generally be reformatted between sector sizes with a low level format, while SATA drives cannot. So a 4Kn SAS drive has a route back and a 4Kn SATA drive does not.
Array pulls, 520 byte formatting and dual actuator drives
Two things surprise people who buy or sell drives pulled straight out of storage arrays, and both are worth knowing before a pallet moves.
The first is non standard sector sizes. Some enterprise arrays format their drives to 520 or 528 byte sectors, using the extra bytes to carry their own integrity data. A drive in that state will not be recognised normally by a standard controller and has to be reformatted back to a standard sector size before it is usable. It is not a fault and the drive is not damaged, but if you have a pallet of array pulls it is worth saying which array they came out of, because that answers the question before anybody has to discover it.
The second is dual actuator drives. The Exos 2X family carries two independent actuator assemblies inside one drive and presents itself to the host as two logical devices. A buyer who does not expect that will report the drive as being half its stated capacity, twice. It is a feature, not a fault, and it belongs on the list.
What is in circulation
The families you will meet.
Placing your hardware in the right family does most of the work of describing it. Each note below says what separates that family from the one above it.
Exos X
The high capacity 3.5 inch nearline line, numbered by generation as X10 through to the current parts. This is the bulk of what moves out of storage refreshes.
Exos 7E
The mainstream nearline line at lower capacities, 7E8 and 7E10 in 3.5 inch and 7E2000 in 2.5 inch. Same market as Exos X, different capacity band.
Exos 2X
Dual actuator drives that present as two logical devices from one physical drive. List them as such, because a buyer expecting one device will report the capacity as wrong.
Exos 10E and 15E
The 2.5 inch mission critical drives at ten and fifteen thousand revolutions, successors to the Savvio name. A performance market rather than a capacity one.
Nytro flash
Seagate's SAS and NVMe solid state line. Part numbers begin with X rather than ST, which is the quickest way to tell a Seagate SSD from a Seagate hard drive on a list.
Constellation ES and Savvio
The names Exos replaced. Constellation ES became the nearline line and Savvio became the mission critical one, and both names are still on drives in circulation.
IronWolf, SkyHawk and BarraCuda
The network attached storage, surveillance and desktop lines. Not enterprise nearline, and they routinely turn up inside mixed pallets, so list them separately.
Exos AP and CORVAULT
Seagate's own application platforms and storage systems, built around the same drives. These are enclosures rather than drives and belong on the storage side of a list.
The same categories, every manufacturer
The families above are this manufacturer's own lines. The category pages carry the wider list, everything that circulates in each category whoever built it, with the part number prefix or physical marker that identifies each one. They are identification help rather than stock lists.
None of this is a stock list
Every model name and part number on this page is identification help for the reader. None of it is a stock listing, and nothing here says that GTR Supply holds a particular item. Send the part number and the quantity you need and we will tell you where we stand.
What it is worth
What decides the number.
Condition is only part of it. These are the things that genuinely move a valuation in this line, and most of them are still in your hands when you write the list.
- Capacity band, since high capacity nearline drives clear faster than small legacy sizes whatever their condition
- Interface, because SAS and SATA versions of the same capacity serve different buyers
- Sector format, which is invisible from the capacity and decides whether a drive can join an existing array
- One capacity in real volume rather than a spread of odd sizes across a pallet
- Whether the drives are still in their sleds or caddies, since a bare drive needs a tray bought for it
- Labels intact and readable, because the ST number is the only thing that identifies the exact part
- Whether the drives came from an array that formatted them to a non standard sector size
- Self encryption and secure erase variants, which are encoded in the part number and narrow who can use the drive
- The whole pallet offered as it stands rather than one that has already been picked through
Both sides of the desk
We supply it, and we buy it.
If you are buying
On the selling side GTR Supply supplies enterprise nearline and mission critical drives in volume, tested, graded and securely wiped, shipped by the pallet against a full manifest. Send the part number and the quantity you need and pricing normally comes back the same business day. If you are extending an array rather than building one, send the sector format your existing volume is running on and the drive model already in it, because a healthy drive of the correct capacity that reports the wrong logical block size is not a usable replacement and that is the single most common way a drive purchase goes wrong. Say as well whether you want drives in caddies or bare, since trays for some platforms cost more than the drives. Every drive ships with its SMART health data on the manifest. Nothing on this page is a stock list.
If you are clearing
On the buying side GTR Supply buys used Exos and other Seagate enterprise drives in bulk, in caddies or bare, sorted or mixed, tested or with no test data at all. Untested is genuinely fine and no testing is required before you write. What speeds up a valuation is a breakdown by part number, or at least by capacity and interface, with a count against each line rather than one total for the pallet. If reading several hundred labels is not realistic, photograph one label per stack and give rough counts. Leave the drives in their sleds and keep the screws with them. Every drive is securely wiped and a certificate of destruction is available on request, and if the drives have to be physically destroyed rather than wiped, say so, because it changes both the collection and the valuation.
Common questions
Seagate Exos, answered.
How do I read a Seagate ST part number?
It reads in three parts. The digits straight after ST are the capacity in gigabytes, so ST16000 is a 16TB drive and ST600 is a 600GB one. The two letters after that identify the family: NM is the 3.5 inch nearline enterprise line where Exos sits, NX is its 2.5 inch equivalent, and MM and MP are the 2.5 inch mission critical drives. Outside enterprise you will meet VN for network attached storage, DM for desktop and VX for surveillance.
The short group at the end is the part everybody truncates and it is the part that matters most. It identifies the interface, the sector format, the cache and whether the drive has self encryption or secure erase features.
That is why two drives with the same capacity and family name can be entirely different parts. When you write a list for GTR Supply, copy the whole string rather than the first half, or photograph the label. One photograph per stack plus a count is enough.
What is the difference between 512e and 4Kn drives?
It is the sector size the drive reports to the host. A 512e drive stores data in 4096 byte physical sectors but reports 512 byte logical ones for compatibility. A 4Kn drive reports 4096 bytes logically as well. Older 512n drives use 512 bytes for both.
The difference is invisible from the capacity and it is decisive. A storage array or pool built on one logical block size will not accept a drive using the other as a replacement. The drive is healthy, the capacity matches and the rebuild refuses to start, and many controllers will not mix the two in one volume group at all.
One practical difference between interfaces is worth knowing. SAS drives can generally be reformatted between sector sizes with a low level format, while SATA drives cannot, so a 4Kn SAS drive has a route back and a 4Kn SATA drive does not.
If you are buying to extend an existing array, tell GTR Supply what your array is running before anything is quoted.
Do you buy drives pulled straight out of a storage array?
Yes, and array pulls are one of the more common ways drives arrive. Two things about them are worth flagging on your list, because both change what happens next rather than whether the drives are wanted.
Some arrays format their drives to 520 or 528 byte sectors, using the extra bytes for their own integrity data. Drives in that state are not recognised normally by a standard controller and have to be reformatted before use. It is not a fault and it does not make them unwanted, but saying which array they came out of answers the question before anybody has to discover it.
The other is that array pulls usually arrive in the array vendor's own sleds. Leave them fitted. A drive in its sled goes straight back into the chassis family it came from, while a bare drive needs a tray bought separately, and trays for some platforms cost more than a used drive is worth.
No test data is required. Untested pallets are normal here.
Guides
Identifying it is half the job. These cover what a buyer actually does with your list once you send it, and what the words on a quote mean before you agree to any of them.
What to Check Buying Used Server Drives
How much life is spent, has it begun failing, and can you verify it. In that order, before price.
Drive Interfaces: SAS, SATA, NVMe and U.2
Start at the backplane, not at the drive. What your controller accepts is the question that costs money.
What Is a Hardware Lot Manifest
The document that lets you price a mixed lot line by line instead of guessing at an average.
Hardware we hold
Clearing it rather than buying
Trademarks
All product and company names are the trademarks of their respective owners. GTR Supply is an independent trader with no affiliation to, authorization from, or endorsement by any manufacturer named on this page.
Tell us the part number and the quantity.
Buying or selling. Send what you are looking for, or a photograph of what you are holding, and we will tell you where we stand. Pricing and valuations normally come back the same business day.
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