8 MB buffer hard drives question.

[IvanPro]

Which are the real improvements over performance with 8 MB buffer hard disks? I've searched this info everywhere (from web sites of manufacturers to Google with various keywords) but I haven't found anything. Anyone here has this bit of info or can point me to a place where I can find it? I need this in order to decide if I really need to buy an 8 MB buffer model or if I should instead stay with 2 MB buffer models... Thanks.

[DSwain]

That's a pretty good question, and i have an idea. I don't know that i'm correct, but it would probably improve virtual memory use. It would have much more buffer to use than virtual memory, so it would allow you to keep doing more tasks with less virtual memory, rather than the standard 2mb buffers. that's what i believe it is, but not positive.

[bwkaz]

The "buffer" in question here is a chunk of memory on the hard drive itself that buffers requests.

The drive itself is extremely slow (since it's mechanical) compared to the rest of the system. If you had to wait for the rotational latency on every request you'd never get anything done. So the drive caches some previous requests, and reads ahead on requests that miss in its cache. The data that comes off the drive (or gets written to it) is also copied to this cache memory (the "buffer").

When the next request comes in, the drive checks whether it's in its cache before looking on the hard drive. If it is, it uses the (much much faster) cache rather than rotating the spindle around to get the data off the platter.

A bigger cache will give you space for more stuff (duh ;)). The more stuff you can fit in the onboard memory in that drive, the quicker it'll be, on average at least (it depends on the cache hit rate too).

However, even most of this is moot with well-designed operating systems (i.e., Linux and anything else that has OS-level buffers and filesystem cache), because these OSes will have their own cache in system RAM, which is even faster than the hard drive cache (because there's no trip on the PCI or IDE bus for memory reads). These OS caches are going to be much larger than 8 megs anyway (Linux will use almost all of your RAM for this if nothing else is using it).

So it's good if you're hitting the drive all the time. But if your OS is going to take some disk reads and satisfy them from the memory caches instead, then it won't matter nearly as much. The initial load of some things may be a bit faster, but probably not because once it's in the hard drive's cache, it's also in the OS cache.

*shrug*

[DSwain]

there ya go, an actual good explaination of it.

[Fryguy8]

From what I understand, it shows noticeable improvements in benchmarks under windows. Not sure how the linux caching will affect it. Also keep in mind it's usually only ike $10 more or less, so I'd just go ahead and get it

[IvanPro]

Thank you all for your kind replies.

I'm writing back again for two reasons: first, because I wanted to ask if everyone knows about desktop new desktop hard drives featuring a double bank memory cache of 8 MB, thus increasing the total cache to 16 MB of which my dealer is so proudly talking about (and of which I haven't been able to find any info); second, because I wanted to share with you all this link:

http://parapet.ee.princeton.edu/~sigm2002/papers/p284-zhu.pdf

Here is expressed a nice and VERY interesting point of view about the increasing size of cache in hard disks:

Hope you find it useful.

Ivan.

[bwkaz]

From this PDF:

In fact, we believe that large disk built-in caches will not significantly benefit the overall system performance. The reason is that all modern operating systems already use large I/O buffer caches to cache reads and writes. Hey, good to know that at least a couple of people agree with me... ;)

[bandwidth_pig]

I have a HD with a 8 meg buffer. A couple of them actually. And frankly, I don't see a big gain in performance. I suppose it depends on what you consider a big gain. I really was dissapointed when I went from a 400 mhz Pentium to a 1.4 Ghz P4 as well (although was pleased with the Athlon). So perhaps I just expect too much. But really, unless your a serious performance enthusiast, I wouldn't really place much emphasis on this. I think the 8 meg buffer is pretty much standard on most of your new larger capacity drives anyway.

Rotational latency? Hehehe. I rather like that term. I just might use that. The rotational latency is inversely porportional to the "favorite term here". I must admit, I have never heard latency used in that context. But it does make sense. Could even be a bumper sticker.

"Linux...for less rotational latency."

[Satanic Atheist]

Just a quicky - I've come across 5400RPM drives and 7200RPM drives and I must say... Is there any real difference because of all this caching? Would it be preferable, say to go for a bigger, 5400RPM drive than a slightly smaller 7200RPM drive at the same cost?

Also, has anyone here come across the 15,000RPM SCSI drives and ever tried benchmarking them?

Any info'd be great, thanks.

James

[mrBen]

7200rpm will be faster than 5400rpm - this is rotation speed, and therefore the information comes round to the heads more times a minute. Cache is more to do with cushioning the speed difference between the system and the drive.

Bear in mind that these days many manufacturers offer more warranty on 8Mb cache drives, which might make the extra price worthwhile. (For instance, HGST offer 1 year on 2Mb cache, but 3 years on 8Mb.)

[Satanic Atheist]

I know 7200 is faster than 5400, but is the difference really noticeable assuming the drive is, say, for a home-user with "average" requirements?

James

[mrBen]

Originally posted by Satanic Atheist
I know 7200 is faster than 5400, but is the difference really noticeable assuming the drive is, say, for a home-user with "average" requirements?

James

Depends on 'average'. The more you use the disk, the more you will notice the difference. Anything that does a lot of disk accessing (which can include games, playing mp3s, and especially video editing) will benefit from the increase.

[bandwidth_pig]

Originally posted by Satanic Atheist
I know 7200 is faster than 5400, but is the difference really noticeable assuming the drive is, say, for a home-user with "average" requirements?

James

I would say it is worth it in this regard to go with the 7200. I was tempted to go with the larger slower drive myself. But it really depends on what you will do with the drive. Are you going to install a OS on it, or just use it for additional storage? And if you are using it just for additional storage, then you have to think about maybe wanting to use it for something else later.

[Satanic Atheist]

I was just curious as to benchmark statistics. I don't use my drive intensively since it's mostly used for the OS (stuffed, but I still use it) and data storage (porn & other stuff).

By normal usage, I refer to someone perhaps in an office or someone at home who does Word documents or surfs the Internet. I don't think the difference would be at all noticeable for Joe Average.

James

[bandwidth_pig]

Hmmm. Ok. I'm glad you brought that up because I have been meaning to adjust some settings. Under defaults, hdparm had this to say about my 7200 RPM.

/dev/hda:
Timing buffer-cache reads: 128 MB in 0.30 seconds =426.67 MB/sec
Timing buffered disk reads: 64 MB in 2.33 seconds = 27.47 MB/sec


Thats without any tweaking. Note the timing-buffer cache reads. Rather pleasant. I did expect better on the timing buffered disk reads though. But I can adjust that. This was default.