About hard drive caches

[Otto Dafe]

What kind of effect does cache size have on the performance/fidelity of a drive? Incidentally, I was just pricing hard drives and it struck me that for a SATA II hard drive you're paying about 25-30 cents a GB. That's pretty freakin' sweet.

P.S. I posted a few weeks ago about my drive slipping to PIO mode, apparently that's a pretty big warning sign, nevermind what SMART says.

 

[Davros]

so now Dereks an expert on hard drives is he

 

[Otto Dafe]

so now Dereks an expert on hard drives is he

Whoa careful man, if you mention him on a message board he will come.

 

[Ateo]

I noticed major preformance benefits going from 8MB to 16MB cache, so I would tink that the bigger cache the faster.

 

[Otto Dafe]

I noticed major preformance benefits going from 8MB to 16MB cache, so I would tink that the bigger cache the faster.

Hmmm...interesting. The price diff is only 64->74. Only thing is I like to use a newer drive for storage and old drive for OS(expendable). But if the new drive has better performance I'd like to put the OS(s) on it(old drive is a 250gb SATA1 8mb).

I may have to rethink my setup somewhat. I used to put the pagefile on the storage drive, but I've got 2gb ram now so I rethought that and was keeping games and thrash heavy apps on storage instead. Man, decisions decisions.

 

[Skrying]

I am sure my 16MB cache for my hard drive helps, I just don't notice it I guess. Sure, it loads quicker than my old hard drive, but it's not some amazing difference or really even that large. However, if the difference is within $10 then there's little reason not to go for it, as the 16MB probably also hints at a newer model that would have other benefits just beyond its cache size.

 

[Otto Dafe]

I am sure my 16MB cache for my hard drive helps, I just don't notice it I guess. Sure, it loads quicker than my old hard drive, but it's not some amazing difference or really even that large. However, if the difference is within $10 then there's little reason not to go for it, as the 16MB probably also hints at a newer model that would have other benefits just beyond its cache size.

That's pretty much where I'm at, I'm just pondering setup...What do you guys do to keep your data safe? I just had a drive fail on me, but thank the gods it was the expendable OS drive. I'm too lazy to make DVD backups, it would be too time consuming to track versions of files. Anyone running a raid array? Thinking about that, hard drives being as cheap as they are it seems like the best option is magnetic, however things get backed up.

 

[Skrying]

That's pretty much where I'm at, I'm just pondering setup...What do you guys do to keep your data safe? I just had a drive fail on me, but thank the gods it was the expendable OS drive. I'm too lazy to make DVD backups, it would be too time consuming to track versions of files. Anyone running a raid array? Thinking about that, hard drives being as cheap as they are it seems like the best option is magnetic, however things get backed up.

Back my data up to an external server. All data is therefore stored to two locations (the computer it was originally from and once a week to a home server). If I did not have such a setup however I would go with possibly mirroring (RAID 1) setup or just a extra hard drive you can back your media files on. Mirroring if you want to go the easy route however.

 

[swaaye]

Personally, I'm surprised they don't stick like 64 or 128 MB RAM on the drive. After all, they just use SDRAM. Large amounts of RAM would probably have diminishing returns considering they need to reasonably maintain data safety, and putting it in RAM isn't doing that lol.

 

[Skrying]

Personally, I'm surprised they don't stick like 64 or 128 MB RAM on the drive. After all, they just use SDRAM. Large amounts of RAM would probably have diminishing returns considering they need to reasonably maintain data safety, and putting it in RAM isn't doing that lol.

Hybrid drives will be like adding another cache between the main memory and hard drive. Though I assume it will be at least 128MB and maybe more depending on prices, etc. Personally I would imagine 2GB worth to be easily within reason for cost these days and would likely happen. It seems like forever though we've been hearing about such drives, I've yet to personally see them.

 

[zsouthboy]

Personally, I'm surprised they don't stick like 64 or 128 MB RAM on the drive. After all, they just use SDRAM. Large amounts of RAM would probably have diminishing returns considering they need to reasonably maintain data safety, and putting it in RAM isn't doing that lol.

Even WITH the diminishing returns, I have a feeling we eventually will see tons of cache advertised and put in, even if it doesn't help anything.

See also: low end video cards with 512(!) MiB RAM

It could be a marketing bullet.

 

[Otto Dafe]

Incidentally, is a hard drive cache lazy, or do they write everything to disk asap?

 

[Simon F]

Incidentally, is a hard drive cache lazy, or do they write everything to disk asap?

Do you mean "write through" as opposed to "write back"? One would assume that the primary use of the cache (when writing to disk) is a buffer to hide the latency of getting the head into the correct location on the disk, but I do 3D not disk technology so feel free to ignore what I say!

 

[Rys]

Do you mean "write through" as opposed to "write back"? One would assume that the primary use of the cache (when writing to disk) is a buffer to hide the latency of getting the head into the correct location on the disk, but I do 3D not disk technology so ignore what I say!

You're still right (annoyingly ). The buffer is mostly there to hide seek latency (for R and W), or to help implement a prefetch scheme for reads.

 

[Blazkowicz]

you wouldn't want writing to a huge cache and losing the data if there's a bsod, power outage, hitting the reset button etc., would you?

 

[swaaye]

you wouldn't want writing to a huge cache and losing the data if there's a bsod, power outage, hitting the reset button etc., would you?

Yeah that's why I brought up the dimishing returns idea. They can't really just stick your data in that cache and keep it there if it's popular to write/read. I imagine they have to dump it out ASAP cuz losing say 128 MB data would be terrible. So, they use it like Simon F and Rys said, as an intelligent prefetch / seek hider that also puts data back on the drive ASAP.

Now, if it were Flash RAM, they could have a lot more freedom perhaps.

 

[Frank]

Btw, Windows putting it into PIO mode is most of the time a problem with using stand-by mode. Windows doesn't like that, and decides that the HD is broken and should be turned down.

 

[Otto Dafe]

Do you mean "write through" as opposed to "write back"? One would assume that the primary use of the cache (when writing to disk) is a buffer to hide the latency of getting the head into the correct location on the disk, but I do 3D not disk technology so feel free to ignore what I say!

Yeah probably a dumb question, but I was wondering if they were write-back. Only reason is that if the cache is just a FIFO buffer it seems odd that they're scaling them up, without either a) a longer seek time, or b) greater bandwidth. The bandwidth on the 16mb SATA2 I just got doesn't look appreciably greater than the 8mb SATA1 I still have, which prompted the question. Granted, it would be rather insane to sit on data headed to the disk.

Edit: Forgot they might be doing predictive read aheads, but is there even that much logic in there? Can't find anything on google...

 

[Otto Dafe]

Btw, Windows putting it into PIO mode is most of the time a problem with using stand-by mode. Windows doesn't like that, and decides that the HD is broken and should be turned down.

Interesting, I had been using full blown standby mode and the PIO thing is relatively coincident with that. In the end though it abruptly crashed and on reboot I got disk read errors. I still mean to try to recover a few things from it if possible, but it's hard to find a use for a hard drive you don't trust. The little guy was a trooper though, right to the end.