[ale] [OT] spec'ing drives for a NAS

[JD]

On 09/23/2012 11:16 AM, John Anderson wrote:
> I am looking at drives for a home NAS and there are options for 5900rpm 
> versus 7200rpm, sata 2 vs 3 and cache size.
> 
> My intuition is that none of this matters, by the time you transfer the 
> data across the network any differences will disappear.
> 
> Agree? Disagree?


**Strongly disagree** unless your network is slow. If you only have a 100base-tx
network, a $22 GigE switch will make you much happier.  Being stuck transferring
files at 10MB/s sucks.  If you will be accessing over wifi then you are 100%
correct and the HDD doesn't matter.

On a GigE network, I routinely see 70-75MB/s file transfers for 10-20GB files. I
love RAM being used for disk buffers.

OTOH, the NAS device itself probably matters more. Often the low end home NAS
models have processors that are the true limiting factor. Performance oriented
NAS devices, including for the home market, usually have an approved HDD list.
Knowing the model of the specific NAS you are working with might help get better
responses.

All the SATA bus specifications don't really matter for a single spinning disk.
 Those can't flood the bus after the cache is exhausted.  OTOH, if you are using
eSATA with 4+ HDDs, then the bus bandwidth could matter, but probably not with
SATA2 or newer.  We can all do the simple addition - a HDD that does 80MB/s is
640 Mb/s.  3Gb/s is about 4.6 HDDs, so over 4 HDDs sharing the 3Gb/s bus would
make it important.  There are real-world losses, but this is close enough.  All
the specs that I read show "upto" numbers.

Run a few tests with these commands on different disks around your house.

$ dd if=/dev/zero of=zerofile.000 bs=1M count=10000;
$ sleep 30 ;
$ dd if=zerofile.000 of=/dev/null bs=1M

You'll see widely different results. RAID level matters most, but so do other
differences.

I see 9.4MB/s, 22MB/s, 39MB/s, 70MB/s, and 128MB/s across the different spinning
disks here. No network involved.  This is a mix of green, blue and black model
drives across different manufacturers.  The "black" drives are the fastest -
both 70 and 128MB/s results are for black drives either alone or in a RAID set.
 I have a Raptor, but it isn't connected anywhere - it is too small to be much
use. sniff, sniff.

BTW, the 39MB/s was writing to an encrypted partition (7200-blue HDD) on a
laptop tested from inside a virtual machine. Reading from that same encrypted
disk was 82MB/s.

No SSD or flash was tested. These were all spinning disks.  On SSDs, bus
bandwidth will definitely matter.