[clug] Western Digital: some RED drives using SMR, Shingled Magnetic Recording

[steve jenkin]

If you’ve bought WD Red drives for a home or SME NAS in the last while, they may not perform as you expect.

Shingled drives write a wide stripe, intentionally overwriting part of the previous track, leaving a thin but readable track.

SMR drives write to contiguous blocks very well, but “Update in Place” requires reading / rewriting an entire “Zone”.
The concept is closest to Optical Drives (RO or RW) where a volume could be left “open” for updates or  “closed” and nothing more written.

There’s a US class action underway based on this, based on an investigation by Chris Mellor of El Reg.

The chart WD provides has a little surprise (at least for me).
WD’s 2.5” drives, WD-Blue and Black are SMR.

=====================

On WD Red NAS Drives
<https://blog.westerndigital.com/wd-red-nas-drives/>


Current SKU’s using SMR
<https://blog.westerndigital.com/wp-content/uploads/2020/04/2020_04_22_WD_SMR_SKUs_1Slide.pdf>

=====================

Zonefs File-System Will Land with Linux® 5.6
<https://blog.westerndigital.com/zonefs-file-system-linux-5-6/>

 Zonefs is not a general-purpose file-system like the famous XFS or ext4. 
Legacy, unmodified applications will not be able to take advantage of zonefs.

Zonefs allows is to simplify the implementation of zoned block devices support in applications by replacing raw block device file accesses with the richer set of regular file system calls. 
This means, for instance, that developers do not have to rely on direct block device file ioctls, which can be far more obscure.

=====================

Zoned Storage 
<https://blog.westerndigital.com/what-is-zoned-storage-initiative/>
Zoned Storage Devices are block storage devices that have their address space divided into zones. 

ZSDs impose unconventional writing rules:  
	zones can only be written sequentially and starting from the beginning of the zone. 
	In addition, data within a zone cannot be arbitrarily overwritten.

The Linux kernel work on zoned storage started back in 2014 with the most minimal amount of support incorporated into the 3.18 kernel.  
The first kernel release with functional ZBC/ZAC command support was kernel 4.10 in early 2017.   
The support has continued to improve, and the most recent kernels have device-mapper support as well as some filesystem support.

=====================

--
Steve Jenkin, IT Systems and Design 
0412 786 915 (+61 412 786 915)
PO Box 38, Kippax ACT 2615, AUSTRALIA

mailto:sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin