Final night time, a Western Digital govt reached out to Ars to tell us of a weblog post regarding their controversial Crimson drives.
The corporate is taking a brand new branding initiative to make clear the know-how utilized in its NAS drives—within the close to future, “WD Crimson” will completely imply disks utilizing Shingled Magnetic Recording know-how, and “WD Crimson Plus” will imply disks utilizing Standard Magnetic Recording.
This report is the newest in a sequence on laborious drive producers slipping SMR know-how into present disk strains, with little or no discover to prospects.
In (very) transient, SMR disks typically carry out effectively sufficient in gentle storage workloads, with loads of idle time between storage requests—however they will fall catastrophically flat on their faces when hit with extra demanding workloads. The ZFS filesystem, specifically, tends to current SMR disks with challenges they’ve problem dealing with.
Though all three remaining main laborious drive distributors—Western Digital, Toshiba, and Seagate—have “submarined” SMR disks into present channels with out doing a lot to inform prospects about it, solely Western Digital has accomplished so with disks designed particularly for NAS, or Community Connected Storage, use.
Sadly for Western Digital, NAS customers are typically considerably extra technical than basic customers—and so they often hit their disks with far harder workloads than Western Digital apparently examined or deliberate for.
From Crimson to Crimson Plus
Using SMR know-how in Western Digital Crimson shouldn’t be going away—however transferring ahead, “Crimson” will completely imply SMR disks. The present SMR fashions—WD 20/30/40/60 EFAX—will retain their present mannequin numbers and can retain their present WD Crimson branding. In the meantime, the CMR disks previously often called WD Crimson—in sizes from 1TB to 14TB—get a brand new “WD Crimson Plus” branding and label, though their mannequin numbers additionally stay the identical.
Western Digital’s new advertising and marketing for the SMR-equipped Crimson drives labels them as for SOHO use solely and clarifies that this implies low-intensity operations with numerous idle time in between—and no ZFS. For small enterprise, “intensive,” or ZFS workloads, there’s the Crimson Plus line—which successfully simply means the older, pre-SMR fashions for now.
There’s additionally a Crimson Professional line focused to maximum-performance purposes. This line is unchanged—it existed with the identical branding earlier than the SMR fiasco, and it nonetheless exists with the identical branding and identical fashions in the present day.
Understanding SMR limitations
There’s a pretty big CMR cache space on the in any other case SMR disks, in addition to a 256MiB unstable (RAM) cache. Western Digital does not publish particulars concerning the CMR cache space in its product datasheets, sadly—however typical estimates, akin to what was proven on this blocksandfiles interview, vary from 1GiB to 100GiB, relying partially on the dimensions of the disk itself.
The CMR cache space on the drive will carry out the identical as a completely CMR disk does—and if it has “downtime” between storage requests, the drive’s firmware can spend that point studying information from the CMR cache and trickling it all the way down to the significantly extra restricted most important SMR storage space. As soon as completely saved within the SMR zones, the info will be learn at about the identical velocity as it will be from an equal CMR disk—SMR’s efficiency limitations are strictly certain to writes.
For those who by no means dedicated sufficient write operations directly to overflow the massive CMR cache space, and also you gave the drive prolonged quantities of idle time to “breathe,” you’d see no efficiency distinction between CMR and SMR disks—though, as some NAS customers have commented, “you may hear them operating on a regular basis.” This refers back to the rubbish assortment course of migrating information from CMR cache to SMR zones occurring in lengthy idle instances between operations.
Even in the event you commit sufficient giant write operations directly to overwhelm the CMR cache, in our testing Western Digital’s SMR firmware typically does a surprisingly good job of committing writes on to the SMR zones. This good job is based on these writes being giant, contiguous writes, nevertheless—and on them being new writes, not rewrites of present information. With the intention to modify a single 4KiB sector in a 256MiB SMR zone, the firmware should learn in the complete 256MiB zone, then modify that one sector, then write the complete 256MiB zone again out once more.
Is the brand new branding sufficient?
The brand new branding is actually a giant step ahead for extra educated customers who already know they do not need SMR—the one factor they should know is “Crimson” means SMR, and “Crimson Plus” and “Crimson Professional” imply CMR. The brand new branding replaces lengthy tables stuffed with inner mannequin numbers—which could not be mirrored precisely on reseller websites, even when the customers know which of them to make use of.
We’re not sure whether or not the brand new, simpler branding will fulfill the already-ongoing lawsuits in opposition to Western Digital, nevertheless. One US class-action lawsuit alleges that advertising and marketing any SMR disk as “NAS” disks quantities to actionable false promoting. The brand new branding is a giant assist to customers who already know what SMR means and what its limitations are—nevertheless it’s unlikely to do a lot to teach customers who aren’t already within the know.
Our use-case evaluation exhibits that SOHO workloads usually are primarily based on quick durations of entry to the drives. This leads to extraordinarily low common throughput (in contrast with the drive’s obtainable throughput) and supplies loads of idle time for the DMSMR drive to carry out the mandatory background operations, making it an excellent match for this utility.
In broad strokes, we agree with the above quote from Western Digital’s weblog put up asserting the brand new branding. Nearly all of customers shopping for small Synology, Netgear, or different purpose-built NAS gadgets are doubtless utilizing them intermittently, with a small variety of total customers, and principally for big recordsdata akin to digital pictures, films, and music. For these customers, an SMR-equipped Crimson will in all probability be okay—they’re unlikely to push by the CMR cache, and even when they do, the SMR administration firmware can in all probability deal with the direct writes pretty effectively.
The true query transferring ahead is how effectively Western Digital’s weblog put up asserting the brand new branding will tie in with the precise product particulars seen on reseller websites. If there is not outstanding disambiguation between Crimson, Crimson Plus, and Crimson Professional on the product pages themselves, the brand new branding might not attain lots of the individuals who must see it.