just brew it! wrote:
what IS the compelling use case for 2.5" HDDs anyway?
Known retention characteristics and price. I'd be really curious to see hard data on real-life long-term SSD retention.
Retention characteristics are more important for archival media. Relying on your laptop for archival storage seems like a bad idea? And while HDDs do have better retention characteristics it treated well, they are more sensitive to environmental conditions (mechanical shock, temperature, humidity), so in actual use in a mobile device (which is by its nature probably going to be subjected to more abuse) I'm not sure you're any better off?
terabytes of storage in your laptop
That would be nice.
Lots of things would be "nice", but life is full of tradeoffs. I'm perfectly willing to put up with reduced capacity to not have to deal with the abysmally slow (in comparison) performance of a HDD. In a desktop I can put a smaller SSD for OS and applications, and a larger HDD for bulk storage. I don't have that luxury in most laptops, and in that case I'll take the smaller faster drive over the larger slower one, even with the (potential) retention characteristics issue.
Also, this article
suggests there's some CMR "cache" in these SMR drives:
the MTC technology uses several bands of PMR tracks on the platters, around 1 GB of NAND flash cache as well as DRAM cache.
Though who knows if it's just firmware or it requires something physical on the platters.
Yes, drive-managed SMR drives typically have some area on the platters that is used for caching random writes. The drive moves these to the SMR areas in the background. But this is completely invisible to the OS and end user, and (AFAIK) not configurable on any current drives.
IIRC there's a provision in the host-managed SMR drive protocol to allow the OS to specify the split between CMR/SMR areas of the disk, but I don't know if any drive vendors currently implement this. Even if supported, changing the percentage of CMR tracks would almost certainly require a complete reformat of the drive since the tracks will be laid out differently. I believe most host-managed SMR drives currently hard-wire the split with some low-single-digit percentage of tracks at the start of the disks being CMR. And host-managed SMR drives will likely never come to consumer devices anyway, it's a feature aimed at Cloud storage providers and requires specialized file system support (i.e. you're not gonna run NTFS or ext4 on them).