Hard Drive bandwidth

[softwareguy256]

I tried getting some crude benchmarks to see if I should upgrade to a SSD. I basically went to an applestore opened up a command prompt and typed:
grep -r a *
grep -r a * > largefile.txt

and measured the disk activity in activity monitor.
Macbook Air: 250 MB/Sec peak
Macbook pro 17'': 100 MB/sec peak
My 2009 macbook: 18 MB/sec peak <-- wtf?

With an external 10k western digital raptor drive hooked up to usb 2.0 I am getting about 40 MB/sec peak.

At this point I cannot rule out that the macbook logic board is not a bottleneck, which is preventing me from buying a $400 SSD drive upgrade. I read the return policy on Newegg, there is none, only exchange. I would only upgrade if I could get performance similar to macbook air I saw today.

What peak disk access do others with macbooks get?

 

[simsaladimbamba]

I got at least 75 MB/s with my 2008 MacBook and a 160 GB HDD (5.400 RPM). Maybe your HDD is failing?

 

[Intell]

Try doing "cd /" then "grep -r a * > largefile.txt". If there isn't much stuff for it to list, it won't reach its peak speed.

 

[davidg4781]

Hrm. I got 122 on my 2006 CD MacBook. It has a 7200 HDD. If I'm looking at the right place.

 

[throAU]

Your crude benchmark will not take disk fragmentation or file size into account (likely explains why your own macbook is so slow) - many large files = faster than many small files.

However, in terms of IOs per second (which generally is a more useful measure than megabytes per second) under random IO, for reference:

7200 rpm data = ~70-80 per second (this is as fast as the heads can re-position for random reads)
SSD = 4000-8000+ per second (no head repositioning time).


If you're streaming large, non-fragmented files a hard drive will perhaps get 100-120 meg per second (vs say 200-300 for an SSD). If you're doing random 4k reads, that may drop to 300k per second (75-80 IO operations x 4k per sec).

An SSD will stay fast (up around 200 meg per second) doing random IO.


THAT is why an SSD kills for performance in most day to day things - multi-tasking disk access is not totally random, but its not very sequential. Even if your SSD only did 80 meg per second, it will still be faster than a spinning disk for most day to day use, because most day to day use (other than file copies) doesn't involve sequential streaming. Even a "slow" SSD will be far more responsive.


Even if your IO controller on your macbook is a bottleneck, your access patterns will likely be faster with SSD - because peak throughput is not what you're typically doing.



edit:
the raptor on USB getting 40 meg peak is about all you can hope for (USB bus saturated). hook it up to firewire and you'll likely hit 80 meg / sec (firewire saturated). a raptor on anything other than thunderbolt (or SATA) will be bottlenecked by the bus.

Your macbook should have a SATA2 bus in it, which can do 3gigabit. So, up to 300 meg per second, in theory... you aren't currently bottlenecked by the bus.