Hard-Drives with >8MB Cache

[Idontcare]

Other than the obvious "point of diminishing returns", what limits hard-disk drive manfacturers from making larger and larger cache carrying hard drives?

When will we see 16, 32, 64 MB, etc. cache on hard-drives released?

Seems like a natural path of evolution for improved performance, especially since the Spot prices as of 4/07 were:

64 Mb chips (thats 8MB) = $2.23 (US$)
128 Mb (16 MB) = $2.98 (US$)
256 Mb (32 MB) = $4.58 (US$)

So for an extra $2.35 added cost, hard-drive OEMs could mfg hard-drives with 4x max cache currently available.

What are they waiting for?

Edit: forgot some words, the post didn;t make much sense as was

 

[Pariah]

Just adding cache doesn't guarantee performance increase, if the drive isn't properly optimized it won't be much faster and could even be slower. Additional cache does not cost much, but paying someone to optimize the drive to take advantage of it does. The biggest problem with additional cache is data volatility. If you have 64MB of cache on the drive and your system crashed, you could be in very bad shape. Without some sort of battery on the drive, you will not see any drives past 16MB of cache, and those are only AV drives where lost data isn't a major issue.

 

[astroview]

If you have 64MB of cache on the drive and your system crashed, you could be in very bad shape.

Why would that be bad, don't you still have the data on your hard drive?

 

[billyjak]

Windows would have a large amount of Data to dump before it shuts down and when a crash occurs it's lost.

 

[Idontcare]

Originally posted by: Pariah
Just adding cache doesn't guarantee performance increase, if the drive isn't properly optimized it won't be much faster and could even be slower. Additional cache does not cost much, but paying someone to optimize the drive to take advantage of it does. The biggest problem with additional cache is data volatility. If you have 64MB of cache on the drive and your system crashed, you could be in very bad shape. Without some sort of battery on the drive, you will not see any drives past 16MB of cache, and those are only AV drives where lost data isn't a major issue.

Interesting. But your argument for risk of data loss extends to the entire system, which will have generously many times more ram than the hard-drive cache, even with 64MB, no? The increase in risk is a drop in the bucket. Who thinks twice about this increase in data loss risk when adding a stick of 128MB or larger ram to their system?

For performance, I'm positive your comments are valid as anything is better optimized than not optimized, but are re-optimizations required to see performance improvements in software or hardware when people drop an extra stick of ram into their systems?

 

[Pariah]

The increase in risk is a drop in the bucket. Who thinks twice about this increase in data loss risk when adding a stick of 128MB or larger ram to their system?

The risk is different with a hard drive. Most of the data in system RAM is not data you would be worried about losing or if you do it's your fault for not saving often enough. With a hard drive, they pretty much all use write back caching now instead of write through caching which means the drive will store data in cache until the drive is free for writes. In essence, you can save a file and it will be stored in cache instead of being written straight to the drive. So there is actually the possibility of losing data you actually thought you saved.

For performance, I'm positive your comments are valid as anything is better optimized than not optimized, but are re-optimizations required to see performance improvements in software or hardware when people drop an extra stick of ram into their systems?

System memory and HD cache are used much differently and are not comparable.

 

[Cosmic_Horror]

do hard drive cache use the same sort of memory chips as found on system memory sticks? eg do they use Sdram, ddr sdram etc etc?

 

[Idontcare]

Originally posted by: Pariah The risk is different with a hard drive. Most of the data in system RAM is not data you would be worried about losing or if you do it's your fault for not saving often enough. With a hard drive, they pretty much all use write back caching now instead of write through caching which means the drive will store data in cache until the drive is free for writes. In essence, you can save a file and it will be stored in cache instead of being written straight to the drive. So there is actually the possibility of losing data you actually thought you saved.

Versus the data in the system ram that you'd lose if the same system were to crash just prior to you saving to a hard-disk? Versus the risk of losing data stored in a 8MB cache-ram on the hard-drive? A 2MB cache? Has anyone EVER lost data because it was written to their 8MB hard-drive cache BUT the hard-drive/system crashed and the only reason they lost their data was because the hard-drive cache didn't flush? I'd laugh, but my head hurts...

System memory and HD cache are used much differently and are not comparable.

Really? I'm not going to touch this one. At some point nothing is comparable unless it is identical, I'm not sure where you think your logic is going.

From what I can tell Pariah, you are saying 8MB cache hard drives shouldn't, nay can't, exist. Or is there a "risk threshold" that wasn't crossed in going from 2MB to 8 MB caches but will be crossed when extending to 16MB caches? Likewise, apparently the utility of ram on mobos, video cards, and hardrives are so completely unrelated as to render all comparisons regarding bandwidth, speed, performance, and cost invalid, at least "not comparable" in your own words. Very intersting, very interesting indeed.

Per Will Ferrell on Saturday Night Live when acting as Alex Trebek in the Jeopardy skits "...and the show has reached a new all-time low..."

EDIT: Spelling

 

[Idontcare]

Seriously though, c'mon guys, surely there is a technical reason why the drives aren't being made with larger caches or at least entertained. I was hoping someone had read some rumor mill stuff and provide some links.

I know the 1st WD drive with 8MB cache was possible due to a fluke in the coding NOT preventing the use larger sized cache. But given the speed bump in going 2 -> 8MB it just seems unlikely that no-ones out there building prototypes with 16 MB or larger. Unless I'm completely missing something such as the data integrity issues Pariah has raised.

 

[Pariah]

do hard drive cache use the same sort of memory chips as found on system memory sticks? eg do they use Sdram, ddr sdram etc etc?

Standard SDRAM

Has anyone EVER lost data because it was written to their 8MB hard-drive cache BUT the hard-drive/system crashed and the only reason they lost their data was because the hard-drive cache didn't flush? I'd laugh, but my head hurts...

Believe or not there are people out there that use their computers for more than gaming and downloading porn. Your data may not be that important but someone who's computer (more likely server) is regularly writing to the disk it doesn't take pinpoint timing to lose data. With 8MB, it doesn't make much difference, but you get up to 64MB or more the issue gets rather serious.

Really? I'm not going to touch this one. At some point nothing is comparable unless it is identical, I'm not sure where you think your logic is going.

System memory is "brute force" caching. You keep adding memory until you exceed what you need. Ask anyone playing Simcity 4, depending on the size of your city having 256-512MB can be practically unplayable while having 1GB the game cruises. Always having more than you need eliminates a lot of the need for optimization. You can't use that method for a HD. Compare it to running Photoshop while editing 100MB files. If you're using 512MB of RAM while doing it, and you have 64MB of RAM in your system, simply dropping another unoptimized 64MB in the system won't make a bit of difference since you are still so far below what you need. There is no practical way to cache an entire HD so you will always be at a severe disadvantage where optimization is your best friend for improving performance. With a HD you also have a point of diminishing returns, while there is a decent chance a drive can exceed the 2MB with read ahead caching, the odds of exceeding 8MB with random read ahead data is much lower.

Or is there a "risk threshold" that wasn't crossed in going from 2MB to 8 MB caches but will be crossed when extending to 16MB caches?

Any halfway decent SCSI RAID controller has a battery backup option. These usually start at 64MB of cache, what the cutoff point below that is, I don't know.

it just seems unlikely that no-ones out there building prototypes with 16 MB or larger.

SCSI had 16MB AV rated models for years. With stress on the "had" part. You don't see them anymore except for the Barracuda 180. Apparently they weren't as grand as you seem to think they would be. Then again, what do those guys know, all they do is make HD's for a living, you're the one with all the brilliant smart ass answers.

 

[Sahakiel]

If I had to take a guess...

I would say the reason for the lack of high-cache sizes is squarely due to diminishing returns.

Well-written programs are designed to access the hard drive as little as possible. In fact, they're written so that critical loops are as small as possible to fit entirely within CPU caches or at most, the RAM. Hard drives are used only to access data that has not been loaded, data to be stored long term (relative to computer cycles), or data that just doesn't fit in RAM (large data streams).
My guess is most of the performance increase from 2MB -> 8MB probably comes from muti-tasking. The larger cache may allow more data to be written or read during the time it takes data and commands to propogate. Just a guess.
Eventually, 16MB drives will come to market and exhibit marked performance increases. However, that may take a while. If you think 2MB is small, just think of when 512k was a godsend.
I also think the recent influx of 8MB drives isn't entirely due to meeting market demand. I heard a rumor somewhere that DRAM manufacturers are having trouble staying in the black. To cut costs, some stopped producing older, lower density chips. This resulted in a shortage of 2MB chips, which really forced hdd manufacturers to use 8MB chips just to have something to put in their drives. Plus, they get to charge more per drive, so I guess it wasn't so much "forcing" as "led."

On a side note, I would love to have massive cache on a drive. However, at a certain point, it would be more feasible just to get a solid state disk, since that's the whole point behind increasing drive cache. One has to remember that disks are very slow (relative to CPU time) devices, so even putting more cache wouldn't help if the data just can't be fed that fast to begin with.

 

[sharkeeper]

Serious gains can be achieved with large caches and delayed writing to disk from that cache. Unfortunately, without the firmware to support this as well as a battery to keep the data intact, the risk of data loss/corruption is very real. Current 2MB and 8MB buffers are nothing compared to the 128~1024MB+ of large RAID HBA's. When you put that much ram on a HDD, it's going to cost serious money. If you want high performance, get a real solution (aka SCSI RAID with lots of cache with BBUM) and you're done.

Sorry, as good as it sounds, you won't see HDD's with SODIMM sockets on the bottom where you could put a 256MB DDR SODIMM for caching. It's not that simple.

-DAK-

 

[Intelman07]

I don't think they need to waste time on more cache. This is enough. They need to work on solid state drives . hehe.

 

[Jhhnn]

I'd go with Sahakiel- for whatever reasons, 8mb seems to be the PODR, something that's obviously subject to change. The PODR concept is easily lost in the shuffle, particularly among enthusiasts, guys who'll spend $50 on a monster hsf to overclock their processor to the same speed as a processor that cost $50 more in the first place won't follow it with any enthusiasm...

 

[stonecold3169]

There are definitely 16mb cache notebook drives, I'm guessing to make up for the low spin spins. However, I remember seeing that the extra cache didn't add much of anything to performance, and got beaten by the 8mb drives in some tests

 

[toant103]

Originally posted by: Idontcare
Other than the obvious "point of diminishing returns", what limits hard-disk drive manfacturers from making larger and larger cache carrying hard drives?

When will we see 16, 32, 64 MB, etc. cache on hard-drives released?

Seems like a natural path of evolution for improved performance, especially since the Spot prices as of 4/07 were:

64 Mb chips (thats 8MB) = $2.23 (US$)
128 Mb (16 MB) = $2.98 (US$)
256 Mb (32 MB) = $4.58 (US$)

So for an extra $2.35 added cost, hard-drive OEMs could mfg hard-drives with 4x max cache currently available.

What are they waiting for?
Go with SCSI. up to 16MB of cache


Edit: forgot some words, the post didn;t make much sense as was

 

[FearoftheNight]

Has anyone EVER lost data because it was written to their 8MB hard-drive cache BUT the hard-drive/system crashed and the only reason they lost their data was because the hard-drive cache didn't flush? I'd laugh, but my head hurts...

Believe or not there are people out there that use their computers for more than gaming and downloading porn. Your data may not be that important but someone who's computer (more likely server) is regularly writing to the disk it doesn't take pinpoint timing to lose data. With 8MB, it doesn't make much difference, but you get up to 64MB or more the issue gets rather serious.

WHO uses it for more than gaming and downloading PORN!?!?!??! There are people like that? =O!!!!!!