Macos – Monitor disk I/O for specific drive in OS X

Generally, no

Specifically, some enclosures can have limits relating to the SATA/IDE controller built into the enclosure.

All 2.5 inch HDDs I've seen have roughly the same power consumption (depending on 5200 or 7200 RPM mainly). Every single one I could operate with the 2 USB cables included with the external hard drive cases. If I plug it into the back of the PC I often only needed one USB cable. Using plugs on USB hubs will often cause problems, though.

USB sockets, per specification, can output up to 500 mA.

Practically 2.5" hdds could use from 600 to 1100 mA for running up. The high power consumption for this short time is - most of the time - allowed by motherboards. When running they will need about 250 to 400 mA, so they are way into the USB specification there.

3,5" hdds will NEVER work from USB alone, since they need +12V power and for a conversion there just aren't enough ampers!

I've seen a few 4Kn SATA drives working in the hard drive validation industry, but I wasn't aware they were shipping any to customers, due to the limited hardware and software support for them and lack of customer demand.

There are two competing mappings for physical vs. logical sector sizes. The Long Logical Sector feature allows a device to have logical sectors longer than 512B (e.g. 4Kn), and the Long Physical Sector feature allows a device to have multiple logical sectors per physical sector (e.g. 512e), though they are not necessarily mutually exclusive. If the manufacturer is claiming the drive is 4Kn, the older controller may providing an emulation layer, like read-modify-write, for older applications and hardware, as older systems simply don't support the 4Kn format.

The sg_sat_identify command from the sg3_utils package would probably give you the information you need (check words 106-108 for Physical sector size/logical sector size information).

It doesn't look like SATA drives can support emulation on-demand, per se, but if the drive is indeed using 512e, instead of 4Kn, performance optimization is maximized by the driver (or possibly USB SATA controller) limiting reads/writes to 4K boundaries, e.g. having the transfer start on an LBA where the lower 3 bits are 0, and end on an LBA where the lower 3 bits are 1:

start_lba & 0x3 == 0
end_lba & 0x3 == 1

So, basically, there's no "switch" that can tell the drive to start or stop emulation. From an end-user perspective, your best bet is probably to make sure your drives are using the best file system for whichever mapping your drive uses and to make sure it's aligned correctly. The following site gives a pretty good breakdown of the common file systems and their stats on performance vs. block alignment on different file systems: http://www.ibm.com/developerworks/library/l-linux-on-4kb-sector-disks/index.html