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advantages of 16mb cache
- Thread starter alex paik
- Start date
What a great question!
Part of the problem is that I don't think we know what the cache is used for.
Maybe it's always used to read ahead. Say you read 512 bytes starting at sector 10. Once the drive finds that sector and reads from it, it might want to assume that you're going to keep reading sequentially; while it is responding to you with your 512 bytes, it might be reading the next 2 or 4 or 16 sectors into the cache. When you come back and ask for Sector 11, then it might satisfy your request almost immediately from the cache memory onboard.
Or, maybe it's always used to cache reads and is strictly LRU with no readahead. If you request a read from sector 10, the drive first checks to see if the 512 bytes on that sector are already in the cache. If they are, your read is satisfied from memory. Otherwise, the least recently hit sector is replaced in the cache with a physical read, and your request is also satisfied by that physical read.
I haven't read anything that describes what drive manufacturers are specifically doing with that cache. The answer is probably somehwere between the two extremes that I describe above; some part of the memory is used some of the time for read-ahead, and the rest for LRU. And I don't doubt that the exact algorithm would vary from manufacturer to manufacturer, and even from model to model from the same manufacturer.
Part of the problem is that I don't think we know what the cache is used for.
Maybe it's always used to read ahead. Say you read 512 bytes starting at sector 10. Once the drive finds that sector and reads from it, it might want to assume that you're going to keep reading sequentially; while it is responding to you with your 512 bytes, it might be reading the next 2 or 4 or 16 sectors into the cache. When you come back and ask for Sector 11, then it might satisfy your request almost immediately from the cache memory onboard.
Or, maybe it's always used to cache reads and is strictly LRU with no readahead. If you request a read from sector 10, the drive first checks to see if the 512 bytes on that sector are already in the cache. If they are, your read is satisfied from memory. Otherwise, the least recently hit sector is replaced in the cache with a physical read, and your request is also satisfied by that physical read.
I haven't read anything that describes what drive manufacturers are specifically doing with that cache. The answer is probably somehwere between the two extremes that I describe above; some part of the memory is used some of the time for read-ahead, and the rest for LRU. And I don't doubt that the exact algorithm would vary from manufacturer to manufacturer, and even from model to model from the same manufacturer.
Vertigo Acid
2(-log[H+])4u
- Joined
- May 31, 2003
- Messages
- 12,410
Doubling the cache means that the drive is twice as likely to find what it needs in cache. How that translates into real-world drive performance, I don't know. I wish SR would get a 200gb DM10 w/ 8mb and a 200gb DM10 w/ 16mb and do a shootoutferrisnox said:
Sorry to bump such an old thread, but between the 2500JS at $83 and the KS at $90, which would you guys recommend? I already have one 2500JS in my system, but need some more space and I'm down to these two (unless there's a really good sale that comes along on a bigger drive)...or would it be worth it to pay $235 ($265 - $30 MIR) for the 5000KS? I could find a way to fill it I'm sure, haha (always do 
).
Thanks for any replies...looking to order this tomorrow.
).Thanks for any replies...looking to order this tomorrow.
- Joined
- Feb 8, 2005
- Messages
- 13,404
You might want to check this thread out first. Damned good prices on WD drives. Anywho, with a difference of what, $7? I'd go for the faster drive.