SMR drives Sold without Disclosure ( Submarining)
If you have been following the online forums, there have been multiple reports on SMR drives being shipped by a few vendors without disclosing this fact. Here is the full scoop on this
What the fuss is about
Technology used in Hard drives today is PMR - Perpendicular magnetic recording. There are two major PMR technologies that exist today - SMR (Shingled Magnetic Recording) and CMR ( Conventional Magnetic Recording which is like PMR V1.0)
SMR can get you a higher capacity drive at a lower cost , but SMR drives are slow with Random writes. Though they are at par with CMR drives in Sequential writes and reads.
Now some vendors have started to ship Slower Sequential SMR drives without disclosing the true nature of the drives- that's the scoop.
Slow Random writes + Problematic RAID Rebuild
SMR drives will pose biggest problem when you are rebuilding the raid. Because of the slower random writes, people have reported that they had problem at the time of resilvering/rebuilding of the RAID. The biggest problem is when you mix a CMR drive with SMR drive. This is confirmed by Vendors like Synology who have listed the newer part numbers as compatible, but with a Cautious footnote
Which Drives are SMR
Out of our portfolio
- WD Red 2-6 TB drives are SMR
- WD Red 8TB+ are CMR
- WD Red Pro are Still CMR
- Seagate Ironwolf are CMR
- Seagate Ironwolf Pro are CMR
Specifically WD Red part numbers Ending with EFAX are SMR drives.
Why a Bigger Cache and how a higher transfer rates
Specifically talking about WD EFAX drives ( WD20EFAX, WD60EFAX,WD80EFAX) have higher cache of 256MB. First the incoming data is cached and then written onto SMR drives, this increases the performance of the drives. that's why you see a higher transfer rate in the new series. Now the cache works wonderfully as long as there is a breather in between data writes so the drive can flush the cache. If the drive doesn't have this ideal time, the performance might degrade.
SMR is only half the picture
Now, there are few things that the online articles have not covered. For the purpose of completeness and to be fair, these have to be considered as well
1. These are DMSMR drives. Which means the inside mechanism is shielded and is managed by the drive itself. These SMR drives appear as the normal drives to the host device, and the shingled writing is managed by the drive, its further optimized by caching. Performance is therefore higher than SMR drives.
2. No problem within the workload : Red is intended for Small business /Home NAS with a workload of 180tb/year , Workloads in SMBs are usually intermittent and the drive is ideal for enough time to perform background data management tasks, keeping the intended performance.
3. If your workload exeeds 180TB/year, you should opt for WD red pro or Ultrastar series drives, both of which are CMR.
So far, the only drives which are DMSMR are WD red 2-6TB. According to Vendor these will perform well under the intended workloads of SMR which is intermittent. If you are seriously concerned though, Shift to WD ultrstar drives. They are not insanely expensive and come with 5 years warranty. WD has clarified that they have done their compatibility and other testings before releasing these drives and didn't find any problems.
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