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meerkt
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sat Oct 03, 2020 1:20 pm

SSDs still cost more:
1TB about x2,
2TB about x2.5 to 4

500GB is where it's getting close, maybe x1.5, yet you still have HDDs there, even CMR.

There's also the question of absolute prices. At 2TB the difference is >$100, and more at 4-5TB (removable storage, >9.5mm).
The price difference here is big enough to warrant the different technology.

There's also retention, but I guess almost no one cares about that. :( After all those years still no real data published, AFAIK.

Suggestion: user-switchable SMR/CMR mode.
 
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 12:00 am

AFAIK CMR vs SMR is not a software setting that can be flipped on a dime. :(

I agree with JBI. The main use case for 2.5" drives is laptops and the "mechanical advantage" (the lack of) of SSDs pretty much has taken over that market. Desktop market is well served by 3.5" drives.
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just brew it!
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 5:16 am

@meerkt -

I did say "most" (not all). I mean, what IS the compelling use case for 2.5" HDDs anyway? For me, the far better performance and resistance to mechanical shock makes SSDs a clear win for the vast majority of mobile applications. Unless you have an unusual use case where you really NEED multiple terabytes of storage in your laptop, paying an extra $50 to have a SSD instead of a HDD seems like a no-brainer.

@Flying Fox -

There has been some talk of supporting configurable CMR vs. SMR, but IIRC this has been in the context of host-managed SMR, not drive-managed. It does imply that the underlying hardware is capable of doing it (i.e. it is basically a firmware issue).
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meerkt
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 6:25 am

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.

terabytes of storage in your laptop

That would be nice.

There has been some talk of supporting configurable CMR vs. SMR


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.

Interestingly, there's also a flash cache, though smaller than the now-retired Firecuda models. Makes me wonder if it could be a weak spot in terms of long-term drive reliability. The firmware could surely just take the flash out of the equation if need be, but firmware aren't always smart.
 
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 7:34 am

meerkt wrote:
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?

meerkt wrote:
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.

meerkt wrote:
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).
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meerkt
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 9:09 am

just brew it! wrote:
Relying on your laptop for archival storage seems like a bad idea?

I wouldn't say archival, but I'd want to know stuff won't evaporate if a laptop happens to get some extended off time, even a year or two. And later on, while HDDs may start their life in a laptop, they eventually graduate to nearline/backup storage.

Perhaps these fears are unfounded. Maybe even battered flash will retain data just fine for 5 or 10 years1. But I don't like this being a "maybe". Also, another nice to have: better (well, any) visibility on cell refresh status and progress.

1 Though I'd prefer more. Data storage and inherent self-destruction are contradictory.

Even if supported, changing the percentage of CMR tracks would almost certainly require a complete reformat of the drive

Wouldn't be a real problem. Get a new SMR drive, switch to CMR for -20% capacity, initial format, and Bob's your uncle.
Last edited by meerkt on Sun Oct 04, 2020 9:49 am, edited 2 times in total.
 
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 9:35 am

meerkt wrote:
just brew it! wrote:
Even if supported, changing the percentage of CMR tracks would almost certainly require a complete reformat of the drive

Wouldn't be a real problem. Get a new SMR drive, switch to CMR for -20% capacity, initial format, and Bob's your uncle.

Given the intended target market I doubt such a feature would get used much though. Enterprise/Cloud users are just gonna order CMR drives if they want CMR drives, and with 3.5" you have that choice.
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meerkt
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 9:50 am

A single model that caters to more markets could be an advantage.
But nowadays they indeed seem to favor more segmentation, at least in 3.5".
 
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Re: 2.5" 9.5mm non-SMR >1TB HDDs?

Sun Oct 04, 2020 1:20 pm

meerkt wrote:
A single model that caters to more markets could be an advantage.
But nowadays they indeed seem to favor more segmentation, at least in 3.5".

Yes, if they wanted to reduce the number of different models we wouldn't have the ridiculous degree of segmentation we have now.

Plus, having a user-configurable setting which will cause the drive to appear to malfunction (or have lower than advertised capacity) if the setting is misconfigured is a recipe for unnecessary RMAs if those drives get sold in consumer retail channels. Again, if configurable CMR/SMR becomes a thing, it'll almost certainly be an enterprise-only feature.
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