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Question on SMR drives

Western Digital Drives - The Preferred Drives of FreeNAS and TrueNAS CORE

etnica

Junior Member
Joined
Aug 2, 2021
Messages
12
Hello,
have a question about SMR drives which I had little knowledge on when buying my WD drives.

From reading I understand that the problem is mainly showing up on slow resilvering when replacing drives.

Question is if I replace a broken SMR drive with a CMR drive will the resilvering perform better then, or is it affected if any drive in the vdev is SMR?


*This is a home NAS with seldom accessed files so r/w performance is not a big deal in general.
 

Constantin

Vampire Pig
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May 19, 2017
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Given that WD appears to have a free SMR -> CMR replacement option for “NAS” marketed drives, I’d try that first.

every SMR drive in a pool should have an additive negative impact on account of how SMR and ZFS work. once the write cache on a consumer-grade DMSMR disk fills up, the drive goes AWOL until the cache has been written to a SMR zone. By default, ZFS waits until the drive confirms it has written its content to disk. So the whole pool gets occasionally blocked by every SMR drive in it.

the more writes, the worse it gets, hence resilverings with SMR take forever, and that’s if you are lucky enough for ZFS not to declare the SMR drive dead.

In the Future, ZFS may be re-written to better deal with SMR, especially the two varieties (host-aware and host-managed) that allow ZFS an insight into what the drive is doing. However, such drives are presently not sold into the consumer market nor does ZFS support them.
 

Arwen

Neophyte Sage
Joined
May 17, 2014
Messages
1,412
One comment about Western Digital SMR "Red" drives, they appear to have a firmware bug.

Here is what I think is happening:

If the host attempts to read a block it has not written, the drive returns an error. Unlike a CMR / conventional drive, this change in behavior causes ZFS read ahead to fail. ZFS can combine 2 or more reads of separated groups of blocks into one drive read request. This can include blocks ZFS has not written, that are in-between the other, real blocks. Because ZFS is one of the few, (possibly only), file systems that does this, it was the one most affected by this "bug". (It's a bug in my opinion...)


My Seagate 8TB SMR Archive drive that I use for backing up my NAS works fine, but slow. (To be clear, I use ZFS on the Seagate 8TB SMR Archive drive, so I could detect firmware bugs, as well as bit rot.)
 

Constantin

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May 19, 2017
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To me, DMSMR drives are very much like cheap SATA port multipliers or RAID subsystems.

They may work fine in a consumer setting but will eventually wreak havoc when used with storage VDEVs on a ZFS System.

Backup drives are an exception though even there is worry about ZFS freaking out on occasion because the drive just went silent as it’s flushing the cache to a SMR zone.

With what @morganL has mentioned here re: SMR, it’s entirely likely that iXSystems will eventually support SMR drives. HASMR and HMSMR drives are likely to get first dibs and for all we know, may even eventually make decent drives for largely dormant pools.

DMSMR support seems more iffy just because the drive firmware obfuscates what goes on in a drive much like a RAID5 hardware controller presents a big pool, not an individual drive. Similarly, DMSMR combine a RAM & CMR cache flushing to a SMR disk with minimal feedback. No shortage of potentially unhappy things to go wrong there.
 

etnica

Junior Member
Joined
Aug 2, 2021
Messages
12
Thanks for input,
just feels bad to have 4 unusuable WD60EFAX drives.

I guess it's a lottery if it would work, I have read that the WD40EFAX have firmware issues but no info found on the WD60EFAX.

Will trie to see if WD would replace them but I guess those chances are slim.
 

Constantin

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I don’t agree re chances being slim but the responsiveness of WD is likely a function of where you live on the planet. In the US, multiple users here have reported success with getting a CMR replacement for a SMR-using but “NAS” branded WD drive (eg Red). The warranties on the replacement drives were also pro-rated with an extra 2 months over what remained of the SMR warranty.

Aside the obvious time sink that replacement entailed, at least WD did right by them to acknowledge that DMSMR drives are inappropriate in NAS applications. The lawsuits likely helped too. Unfortunately, WD continues to sell / market “NAS” branded DMSMR drives, which should be prohibited given that their own employees have publicly presented that ZFS and DMSMR are unlikely to ever play nice.

At least now WD has to acknowledge that these drives use SMR subsystems.
 
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winnielinnie

Senior Member
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Oct 22, 2019
Messages
546
Pray tell, what exactly is the advantage of SMR over CMR when the price for the same capacity drive is the same? Prior to Chia mining taking off, unless my memory is fuzzy, WD Red and Red Plus drives were selling for approximately the same price on Amazon.com.

In what scenario would someone say "A 6TB CMR drive? No thanks! I need a 6TB SMR drive for this."
 

elvisimprsntr

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Jun 2, 2019
Messages
156
I don't think any end user in their right mind would ever intentionally pick SMR over CMR if they were aware of the potential pitfalls.
Manufacturers found a way to increase storage density, thus capacity without fundamental changes to the media allowing them to separate businesses, OEMs, and consumers out of more of their coins. i.e. driven by pure greed. Manufacturers either completely hid or obfuscated SMR until problems were uncovered in some use cases and were threatened with class action lawsuits.
 

winnielinnie

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Oct 22, 2019
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546
Manufacturers found a way to increase storage density
This is what I don't understand. Correct me if I'm wrong, but (Western Digital) SMR is only available for drives up to 6TB, while consumers can purchase CMR drives up to 14TB.
 

winnielinnie

Senior Member
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Oct 22, 2019
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546
That makes "more" sense, but it raises another question: What does it matter to the consumer? Has there ever been an issue where a 3.5" drive could not physically fit inside a chassis because "It's too 'tall' and has too many platters, and thus cannot fit in the bay." ?
 

Bikerchris

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Mar 22, 2020
Messages
104
This is what I don't understand. Correct me if I'm wrong, but (Western Digital) SMR is only available for drives up to 6TB, while consumers can purchase CMR drives up to 14TB.
Not that I know of (hi, just chiming in), SMR are available at higher disk capacities. 10TB WD blacks for instance are SMR.

All I know is that SMR drives in a NAS, take far longer to re-silver - there are plenty of YT videos on the subject and I've tested it myself during my earlier days of the NAS world. The longer that takes, the greater the risk of a second drive failing, that is bad, you want to do it quickly. I don't think I've seen times when the price was the same for both technologies, unless the recent shortage caused one to cost more than usual and brought it up to the same price as the other, and Chia miners likely didn't care which was which (assumption).

The Kung Fo magic that is SMR is impressive, but it conflicts badly with how a NAS operates. Fine as a second drive in a desktop to store non-critical data, bad for RAID systems.

That makes "more" sense, but it raises another question: What does it matter to the consumer? Has there ever been an issue where a 3.5" drive could not physically fit inside a chassis because "It's too 'tall' and has too many platters, and thus cannot fit in the bay." ?
I think to the average consumer, it doesn't matter. All they want to do is open their wallet and see how much storage they get for the contents. It's not a physical thing (beyond the size of a standardized 3.5" drive), SMR sort of creates twice the capacity for the same drive platter size by overlapping stripes. This is a generalization and I'm not trying to understate the technology, videos like this might help https://www.youtube.com/watch?v=aztTf2gI55k
 

Bikerchris

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Mar 22, 2020
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104
Has it changed?
I must have done a quick google search and the 2.5" must be SMR. Either way, I suspect that they have reverted many of their drives back to CMR to save face. Hopefully the majority of what I wrote was of use.
 

Constantin

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Pray tell, what exactly is the advantage of SMR over CMR when the price for the same capacity drive is the same?
None, except for the OEM who gets to ship a drive with one less platter, two fewer heads, and charge many consumers the same price for a lower-performing drive.

IIRC, SMR gains the OEM about 20% extra capacity via areal density, which adds up to substantial savings, if a drive platter can be eliminated.

Try finding a higher-capacity 2.5” CMR drive now. It’s not easy unless you go after $$$ drives meant for data center use.

I have no issues with SMR drives per se, just a huge issue with OEMs surreptitiously changing their CMR lineup to SMR and not telling their customers about it. Ditto “5900 RPM class” drives that run at 7,200 RPM, consume power, wear, and make heat accordingly, but still perform like 5,900 RPM drives. Not ok.
 

kherr

Member
Joined
May 19, 2020
Messages
50
Western Digital . . . . . . . . " Just say NO "

They have a Massive inability to properly represent what you are buying . . . . .

Saying SMR drives are NAS compatible
Not being able to tell you up front what the RPM the drive is . . . . "It is a 5200 RPM CLASS drive" . . . . geshhhhh . . . . get real . . . .
. . . . . . . .

Are they that embarrassed as to what their drive specs are ??? I attempted to find the REAL RPM of a drive and coudn't find it in any of their documentation.

I used to be exclusively WD ........ you couldn't Give me one ....
 
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elvisimprsntr

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I think everyone has had a bad experience with almost every drive manufacturer at one point or another. Its which manufacturer has messed up more recently.
 

Constantin

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I agree, to an extent.

The measure of an individual or organization is usually not visible when all is going well. Rather, it’s what happens when things are not going well at all.

For example, recall the massive difference between tylenol dealing with a potential poisoning possibility in the 80’s vs. the folk running the Dalcon shield division.

Years ago, customers had the option of punishing bad HDD actors by voting with their feet. But M&A has allowed but three OEMs to remain, creating a oligopoly which has done a fabulous job preventing storage prices from following historic trajectories and which has also forced customers customers to keep buying from every OEM, even if a particular OEM has been a demonstrably bad actor.

Thing is, until there is a personal cost at the c-suite level, I expect these trends to continue. Managing to the short term, little to no long term planning / R&D, etc ensures that the industry will stagnate for the foreseeable future.

SMR is just a symptom of this stagnation.
 
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