Something stinky in HDD-land.

[HankB]

There is quite a discussion on the ZFS-discuss mailing list at the moment regarding SMR drives. (SMR => AKA Shingled Magnetic Recording) The consensus seems to be these are the spawn of the devil, the manufacturers involved refuse to identify the drives involved and they should be avoided at all costs. This has been discussed for about a week now (I think.) and some recent threads are linked below.

https://zfsonlinux.topicbox.com/groups/zfs-discuss/T759a10612888a9d9-Me469c98023e1a2cb059f9391

https://zfsonlinux.topicbox.com/gro...e-too-re-beware-of-smr-drives-in-pmr-clothing

If you don't care to read this (and I admit to having a weird sense of what interests me) the drives to be avoided include the large WD and Seagate NAS drives. There is a database to help ID these drives and it is described as

Someone at r/hardware on Reddit suggested this site https://rml527.blogspot.com/

It's a database of platter types across various OEMs, form factors, etc.

You'll have to search each bottom level page for "smr" to find affected HDD model numbers.

This discussion is in the context of enterprise users running large data stores on ZFS (mostly) on Linux. These drives may not even be available in the normal retail channel. I haven't checked. However this is certainly something I'll look into the next time I buy any HDD. It seems to me that these drives may not be good for the home user either (except for some specialized cases.)

 

[EarthDog]

I'll bite.... why is SMR the 'spawn of the devil'...(mostly in linux). Will you summarize what is going on?

 

[knoober]

This is a timely post for me because I am working towards rebuilding my NAS with ZFS and 8tb WD drives. A quick look shows that the drives most commonly shucked from the WD Easystore (WD80EMAZ) is not in the database so... Whew

 

[Zerileous]

Always so much deception in the storage market.

From skimming the links, it appears that it muck with the ZFS ability to provide redundancy with a low percentage of storage. (i.e. the setups where you have 8 drives and 2 of them can fail at the same time without any data loss, but unlike raid 1, the capacity is much greater than half of the total drives). Seems like the process of restoring that data just causes the whole thing to crash with these drives. At least based on my rudimentary understanding.

I wonder if this has anything to do with all the linus tech tips videos about seagate drives

 

[HankB]

I'll bite.... why is SMR the 'spawn of the devil'...(mostly in linux). Will you summarize what is going on?

The short story as I understand it is that the tracks overlap. Think about how shingles overlap. You can't replace a row of shingles w/out messing with the ones that overlap. The shingled tracks are similar. On an ordinary drive when a block is written, only that block is written. With shingled tracks, all overlapping tracks must be rewritten. This can result in very poor performance when tracks that overlap valid data are written, There's a better description at https://en.wikipedia.org/wiki/Shingled_magnetic_recording and if you google the terms you will get a lot of hits with more information.

The gripe seems to be that manufacturers are hiding this information and people purchasing the drives feel that this is material to performance. Apparently these drives do not work well with the ZFS file system.

Incidentally, SSDs share a similar characteristic. The smallest block of flash that can be erased and written is much larger than the block size used by a file system. Furthermore, to write a block of flash, it must be erased first. It can't simply be rewritten the way (non shingled) magnetic drives are. The problem is not as noticeable with SSDs because flash is a lot faster and they use other strategies to keep this from affecting performance.

 

[Janus67]

https://blog.westerndigital.com/wd-red-nas-drives/

WD's response:

Basically you bought "NAS" drives that are meant for RAID but they aren't really made for that purpose. You should have bought the more expensive Pro/Gold/Ultrastars instead.

Pretty crappy response, in my opinion, especially considering there's an upcharge to buy these drives over Blues and such that one wouldn't care/expect RAID support without gigantic performance hits.

 

[Janus67]

they had a follow-up:

https://blog.westerndigital.com/wd-red-nas-drives/

April 22, 2020

The past week has been eventful, to say the least. As a team, it was important that we listened carefully and understood your feedback about our WD Red NAS drives, specifically how we communicated which recording technologies are used. Your concerns were heard loud and clear. Here is that list of our client internal HDDs available through the channel:



Click here for SKUs to our client internal HDDs using SMR technology.

We’re committed to providing the information that can help make an informed buying decision for as many uses as possible. Thank you for letting us know how we can do better. We will update our marketing materials, as well as provide more information about SMR technology, including benchmarks and ideal use cases.

Again, we know you entrust your data to our products, and we don’t take that lightly. If you have purchased a drive, please call our customer care if you are experiencing performance or any other technical issues. We will have options for you. We are here to help.

More to come.