User article Panic around the hard drive. Or just well thought out marketing (from/for whom)? Part No. 2

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User article Panic around the hard drive. Or just well thought out marketing (from/for whom)? Part No. 2

Part No. 2
..... previous Part No. 1 is available here

Nowadays technologies of recording - PMR:

The most widespread technology standard for data recording on magnetic media since 2005 is Perpendicular recording (or perpendicular magnetic recording, PMR). Reason = optimized recording layer and W/R heads brought more Areal density = better utilization of the 3.5/2.5“ HDD form factor. Toshiba as first vendor prepared 1.8“ HDD with 133Gb/in2 for PMR based HDD, shortly thereafter Seagate in 2006 created the first commercially available 2.5/3.5“ HDD with PMR. ... the race for more and more Areal density had picked up speed.

Picture of PMR principle, sourced from Wikipedia:

In 2013, Seagate introduced shingled magnetic recording (SMR) as the next generation of PMR based data recording. Since then Conventional magnetic recording (CMR) was used for preliminary PMR technology and SMR for second generation of PMR. Then Both CMR & SMR are PMR (based on the orientation of magnets in platter). When you see “PMR only” in the description of an HDD, you can’t distinguish whether the disk has CMR or SMR. And vendors hide such information. Why, if SMR is better? Better for whom?

“With SMR technology, Seagate is on track to improve areal density by up to 25 percent or 1.25TB per disk, delivering hard drives with the lowest cost per gigabyte and reaching capacities of 5TB and beyond.” said Mark Re, Seagate’s chief technology officer. And there was also announced that – „Importantly, SMR can improve reliability by allowing Seagate to use fewer heads and disks to achieve new capacity points. SMR also provides a better value by increasing storage capacity while utilizing the same disk and heads as drive configurations shipping today thereby, providing a more cost-effective approach to increasing aerial density.“

Just remember the relation of the vendor costs and the number of platters in HDD. See that point in SMR? Who is the winner?

Where is the problem then?

Some simplification is needed, for better understanding, so I will use an example based on highway traffic (next three pictures sourced from

1. CMR technology is based on enough width (guard space) of highway lanes (disk capacity), then cars can
securely drive with defined speed and direction, without additional complicated regulations. Reason why CMR can’t provide more highway lanes in the closed environment of a 3.5” HDD form factor = they need more patterns, but they can’t change the dimensions of the HDD box. There are just three possible solutions to it:
  • Keep the maximum possible used platters, then the maximum available disk capacity is defined by max. tracks for the write process. No way to infinitely upgrade. Seems to be we’ve reached the physical possibilities of CMR.
  • Change the HDD form factor to bigger than 3.5“, but can you imagine how this would be done? Who will be first? As you read above it was changed many times in HDD history. Achievable, but really costly for everyone.
  • Upgrade the track technology = more tracks (SMR) or new, totally redefined HDD technology (HAMR, ...).
2. SMR technology is based on really short (tiny) highway lane-width, without the guaranteed space for a car
within a single lane. That is risky, but achievable for really low traffic (low workload). However in regular traffic (when all the lanes are almost full) you need to regulate all cars separately in these lanes to achieve movement for all cars = reason for the existence of DMSMR (device managed SMR = HDD firmware-controlled). The append-only highway lanes (platter‘s zones) are very slow for random writing, so writes are first sent to a cache, and the disk moves this data to SMR parts when idle. And the term „when idle“ is a problem for all who use the HDD with a workload of >180TB/yearly (explained below) . Finally, you have achieved a model of more highway lanes (SMR), but a really slow movement of cars vs the normal highway (CMR). This model has additional advantage for vendors = less patterns. And less platters = less cost for vendors.

Back to disk technology terms - SMR must overwrite adjacent magnetic tracks and then rewrite them. That’s the reason why they’re so slow and why they need a bigger cache for such operations.

An additional problem for NAS users is native Zoned device suppor (ZBC/ZAC commands layer for the SMR) for etx4 file system = doesn’t exist for the DMSMR, as far as I know. Thusly the SMR disk can‘t beat CMR speed with etx4. Even using an SSD cache in your NAS can‘t help you with such a basic issue. Some real tests have confirmed such problems during rsync from the SMR drive, especially if the filesystem wasn‘t mounted read-only with the noatime option. Such test confirms that an SMR drive needs to write a timestamp for each file rsync read, resulting in a significant performance degradation from around 80 MB/s down to 3-5 MB/s plus annoying head wear / clicking noise. Different story is for BTRFS, which nativelly supports a Zoned device (SMR), but you have to purchase an HDD with HMSMR (host managed SMR). If you’re operating a system with BTRFS, you should specifically consider purchasing such HDDs. That way you can get better performance. If you’ve already purchased a disk with DMSMR, you might be sorely dissapointed.

From all the mentioned SMR features I would summarize these points:

  • when your Storage pool is about frequent write and read, then SMR isn’t for you. Because your disk buffer will frequently be almost full (no idle time as basic principle of the SMR). Then the HDD firmware will need to locate a single empty track, or rewrite existing ones to be ready to write long sequential data from the buffer. Which will definitely kill your disk performance.
  • when your Storage pool is about frequent read and casual write, then SMR is OK for you (up to first degradated disk incident, because then you will write a lot of data very, very slowly). E.g. media files for Plex server.
  • Never mix both kinds of PMR (CMR or SMR) into a single storage pool (RAID), you will kill your performance, even more
But vendors have prepared a „better“ recommendation for us, regarding when these SMR HDDs are useful for us and when not. Their recommendation is based on 180TB/yearly workloads in the HDD. First, it seems like magic, because every single vendor uses the same threshold = 180TB/yearly. Or is it a kind of mutual recommendation from all the vendors to us? I feel some kind of strange precedents here, when each independent vendor has the exact same operation conditions.

So let’s understand how the independence of HDD R&D functions:
  • In 2011/12, three mergers (Seagate/Samsung, Western Digital (WD)/Hitachi, and Toshiba/Hitachi) reduced the number of HDD manufacturers from 5 to 3 companies.
  • Follow-up Research report named: Southeast Asia beyond Crises and Traps (2017), stated that Thailand is one of the world’s largest HDD manufacturing bases. In 2012 it held approx. 40% of the HDD global share. In 2018 it was 82%. The sector is dominated by two global leaders, Seagate and WD with more than 50% of production there. We need to speak about dominant R&D association:
  • International Disk Drive Equipment and Materials Association (IDEMA), have HDD R&D in Thailand
  • ASTC consortium exclusively covers members from IDEMA only
  • WD, Seagate and Toshiba – use a collaborative joint R&D in ASTC
  • A really interesting read is this 2019 research: Mergers and innovation: Evidence from the Hard Disk Drive market.
Now’s the time to understand, what the 180TB/year workload threshold means

Simple check using a standard situation:
We will utilize an HDD for just 2 hours/daily with backup between two NASes with the average speed of data throughput 70MB/sec (which isn’t perfect speed on a Gigabit network).

Then we can calculate the total amount of data transported between the NASes (disk groups):
70MB/sec x 2hours = 0,6TB/day x 365 days = 221 TB/year .... which is +23% over the 180TB/year threshold for the SMR disk. Then, following this simple check, the operation model is out for the SMR disk.

We still haven’t mentioned RAID operations and RAID factor penalties for the write operation, when you need to define your yearly workload based on a simple IOPS measurement. Then 180TB/year workload is out of any NAS enthusiast’s group operation model.


SMR with DMSMR is great technology for all NAS owner, when they use such HDD(s) or groups isolated for a specific purpose, e.g. media center source.
In this case heavy workload for written operation isn’t expected. When the read throughput for TV is about 60Mbps = 7.5MB/s. Or for a photo library. With such operation model you will hardly reach 180TB/y and you will be happy with the price per TB.

SMR DMSMR isn’t useful for others who need to utilize their disk more than 2hour daily with the average write speed of about 70MB/sec, because you might experience significant speed decrease. There aren’t enough reviews or tests for BTRFS and SMR disks with HMSMR, which would confirm they are better in such conditions. Obviously, you need CMR disks for all virtualization platforms, cloud platforms or heavy backup operations in your NASes, what was an enabler of NAS purchases in last few years. Never use a mixed RAID disk group with CMR and SMR disks. Ever.

When you’re looking for a new HDD, try to compare the number of platters in the watched disks, then if one has SMR technology described and another has the same disk platters, even same capacity, there is a 99,9999% chance, that both of them use the same technology. Yes, it’s complicated, but useful until vendors start clearly disclosing that information.

I really don’t know if the 3 vendors have any mutual agreements about the “SMR disclosure” in their Disk data sheets, I don’t really care, but it seems to be, that their R&D doesn’t care about the NAS development, especially when they create NAS HDDs. And this is a strong message for the customer’s wallet. But I think, they need to take responsibility for such a managed chaos. I have some recommendations:
  • When you purchase an HDD and you’re looking for CMR and not an SMR disk, but the seller can’t confirm the technology level, put this request into your order (e-shop).
  • If you get different technology as was requested, you can claim this order as wrong. In the EU we have strong regulations for it. It is exactly the same example as with a car purchase with a petrol engine and your dealer delivers a diesel engine. Different technology for different driving purpose. And hidden during the ordering process!
  • If vendors don’t care about customers, they will care about claims from their distribution channels, when people massively return their goods, which were different from order specifications.
Protect your purchasing rights!
still waiting for Syno support confirmation about Synology HMSMR support in case of BTRFS = if Synology will recognize such HDDs
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this is was my request to Syno Tech support:

Title: usage of SMR HDD with HDSMR for BTRFS in RAID or SHR - tested scenario by Synology

Do you have tested scenarios for such setup? What was your results and what is your recommendation for such setup. Pls don't write simple 180TB/Y treshold about it.
1. SMR HDD with HMSMR, filesystem BTRFS, in RAID (0,1,5,6,10) or SHR(1,2)
2. basic volume based on single SMR HDD with HDSMR, filesystem BTRFS
3. same for SMR with DMSMR
A. Is there fully supported Host managed SMR disk in Synology NASes?
B. What was performance for SMR with DMSMR? Or define your experiences.
Please, you can use deep dive kind of language in the answer.
Answer (Copy/Paste):
We dont even support SMR HDDs and explicitly list them as incompatible
So do not use SMR HDDs on Synology devices.
Screenshot from the provided link:

My Consideration about such answer:
Seems to be this answer has been provided from someone who doesn't have deep knowledge about the SMR technology, because:
- you don't need any specific support from any HW vendors (NAS, PC, ...) when you will use DMSMR (as you already know from the blog)
- as usual I need push them for answer to my question, because I'm not satisfied from general answer.
I found here list of SMR and CMR - WD Red NAS Hard Drive:

WD10JFCX (1TB) ... 16MB cache
WD10EFRX (1TB) ... 64MB cache
WD20EFRX (2TB) ... 64MB cache
WD30EFRX (3TB) ... 64MB cache
WD40EFRX (4TB) ... 64MB cache
WD60EFRX (6TB) ... 64MB cache
WD80EFAX (8TB) ... 64MB cache
WD100EFAX (10TB) ... 256MB cache
WD101EFAX (10TB) ... 256MB cache
WD120EFAX (12TB) ... 256MB cache
WD140EFAX (14TB) ... 512MB cache

SMR .... each with 256MB Cache

but follow official WD Product list each of them have 180TB/y Workload rate
and as we know, all the SMR disk have 180TB/y Workload rate limitation
Then, there isn't 100% sure, that CMR is real CMR

Official Workload rate definition from WD:
Workload rate is defined as the amount of user data transferred to or from the HDD. Workload rate is annualized
(TB transferred x (8760 / recorded power-on hours))
then all write and read IOPS must be taken into account :) OMG it's less than 2hours of such HDD operation per day in 70MB/s
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how to easy check how many platters do you have in your current HDD:
hdparm -I /dev/sda   .... sdb or sdc ... up to number of your HDD

Result = 16 heads

Naturally in PMR technology, a platter has 2 sides and thus 2 surfaces on which data can be manipulated
Then usually there are 2 heads per platter.
Follow above "hdparm" result. You have 16/2= 8 platters
The you can see what is the RAW size of your HDD, from same hdparm command:

Now you need to calculate, what is RAW value in MB in single platter for a comparison with another HDD (CMR or SMR).
- Device RAW size = 953 869 MB
- Platter RAW size = 953 869 / (8 platters) = 119 233.625 MB/platter = 116.44GB/Platter

So what about make a table such this (columns):
- Vendor
- Disk model (e.g. NAS Red)
- Form factor (3.5"/2.5")
- Model number, achivable from the hdparm results
- Firmware revision, dtto
- Device size (RAW), dtto
- Cylinders, dtto
- Heads, dtto
- Platters based on Heads/2 formula
- RAW size per platter based on mentioned formula (check)

Then we can easily compare when the HDD have less platter for same RAW size, include the last check parameter. Hm?

I need speak with @SynoMan, how we can build comparison table based on your measurement. It will help each others to check HDD CMR/SMR valiadtion.
Second answer (from same Syno support person):

Good Day,
ofcourse you can use the SMR drives. But they are listed as incompatible here:

HDDs which are listed as incompatible can cause major problems.

Synology has consistently worked with drive vendors to verify and improve compatibility with our storage solutions. After receiving users feedback and based on Synology's testing results, this drive is only suitable for light workload environments and not suggested to use under intensive storage workloads, where undesirable performance may occur under continuous write operations.

Synology is dedicated to providing a smooth and reliable user experience to our users, we suggest to pair your Synology storage solution with a storage medium that is suitable for your intended workload and choose other hard drives listed on the compatibility list.
few consideration in my mind:
- I tried use Syno compatibility list for all my NASes, but I found these incompatible HDDs in DS718+ section only. Maybe they need repair DB for such consistent recommendations. Syno has been informed about it. Be sure when you will use your model for such incompatibility “test”.
- when some users have trouble with these HDDs, is there known clear operation model of such users (workload, filesystem, redundancy, level of used disk capacity, virtualization, snapshot/replica, peaks of performance, network, ...)?

I think, that Syno is loosing every day more important point or time - be a first NAS Vendor who will clearly define a recommendation for usage of the SMR technology, which is really useful for a big group of Storage eaters (based on this blog description). And the first can be only one. I see such chance lose everywhere in any business lines.
I found interesting source of updated Platter size DB (GB/platter) in web, but I need to wait for a share approval confirmation.

It will finally confirm my simplified consideration about relation of platter size (GB/platter) vs use technology CMR/SMR
Since you’re putting a lot of time into this :)

Do you know what’s the difference between these two?
WD100EFAX (10TB) ... 256MB cache
WD101EFAX (10TB) ... 256MB cache

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Since you’re putting a lot of time into this :)

Do you know what’s the difference between these two?
WD100EFAX (10TB) ... 256MB cache
WD101EFAX (10TB) ... 256MB cache


seems to be WD101EFAX (Red series) is clone of Ultrastar DC HC330, because they have same R/N (UVXHA9), but with decreased rpm from 7200 to 5400
and WD100 is pure WD
then there is the reason of difference 101 vs 100 in the product code
previous model has been Helium filled (more platters), current model is based on Air filled (less platters with bigger capacity)

same for the WD102KRYZ (Gold series)

for 100% sure, you need to check R/N
follow official Toshiba announcement from April 28th:

For example, in use cases such as network-attached storage (NAS), where continuous random writing regularly occurs, Toshiba’s current product line for consumers features the N300, which does not use SMR.
there is another issue, based on special disks used for Surveillance recording (more writing than reading), when the disks will use SMR. An example:
7Mbps bandwidth from single camera (24x7)
- 26,3TB/y workload, then this scenario is in range of the 180TB/y for SMR (just for continuous writting and w/o single read operation)
- but the Surveillance system have frequently more than single camera
- then for the 180TB/y workload you can use max. 7 cameras (just for continuous writting and w/o single read operation)
- troubles will come when your disk will be full and you will use re-write for new records. Because in surveillance there isn’t such Idle time (main requirement of SMR technology for sustainable IOPS), then the disk buffer will overflow.
Finally, as yo can see, each read operation will make impact to the total yearly workload = number of supported cameras for such SMR disk will decrease.

You can count what will happen when you will use 5Mpix camera sensor, even with H.265 yo will get aprox. 16Mbps bandwidth = max 3 cameras for 180TB/y range.
Ofc, never mix Surveillance recording with another service in same disk!
Story from Syno support regarding SMR is continuous. Curent status:

“do not use any SMR HDDs for a NAS if the focus is performance.”

it was answer for my repeated question in my opened ticket about native support of HMSMR with BTRFS in Syno NASes (what have to be native supported) without impact to performance. Plus answer to my finding: Syno inconsistency in their Compatibility HDD list for NASes - where I found different statements for DMSMR disks (compatible/incompatible).
yes, already seen

But it will be hard to achieve. Reasons:
- SMR is not bad technology for sequential recording in home environments. On the contrary it's useful for majority of home users who will use SMR HDDs for media storage = large sequential write operation of big files (e.g. movies)
- same for Single file archive (backup) data = large sequential write operation of big files = 99.9% of Home backup sw.
OFC except operation in RAID (SHR), except sync.

Then it will be hardly achieved success for all.

What is more important - till now we haven't an official statement from Synology for HMSMR and BTRFS - a test results. I take it as - bury head in the sand .
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Story from Syno support regarding SMR is continuous. Curent status:

“do not use any SMR HDDs for a NAS if the focus is performance.”
Just curious: has anyone gotten a multi (as in more than two) volume RAID 5 or 6 successfully built with SMR drives? I can see how they might build OK in a RAID 1, and, by extension, in a RAID 10 - but that's just guessing. It's also possible that Synology is just saying that SMR is OK for their single drive (non-RAID) NASes - I keep forgetting them.
But they didn't say "do not use any SMR HDD for a RAID", which implies that they work for some kind of RAID...?
they have traditionally issued official weird statements, not to mention the subjective opinions of people from the helpdesk. And, of course, if we add to this mixture some announcements of companies which are more like a declaration of lawyers than people who understand that, then we have this situation.

RAID5 with SMR is suitable for long and large sequential writing operation = backup of images, ...

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