[gentoo-amd64] Re: Hard drive (installation)

[Duncan]

Henry W. Peters posted on Wed, 28 Aug 2013 15:24:36 -0400 as excerpted:

> So my question is: will an external HD work (I do audio
> editing/recording/graphics) as a system/work space? & more importantly,
> will Gentoo install on such a HD (external, usb 3))

USB-3 bus-speed, 5 Gbit/sec full duplex (previous USB was half-duplex and 
USB-2 was 480 Mbit/sec), tho "reasonable" thruput is 3.2 Gbit/sec (400 
MByte/sec), according to wikipedia, should be much faster than a 
"spinning rust" hard drive, and indeed, should be reasonable as an SSD 
bus, as well, altho SATA 3 (aka SATA 600) is a bit faster (6 Gbit/sec, 
600 MByte/sec), and a good speed SSD bottlenecks on the SATA 3 bus.  By 
comparison, PCIE 1.x is 5 Gbit/sec at 2X, with PCIE 2.x 5 Gbit/sec at 1X 
and PCIE 3.x 8 Gbit/sec at 1X.

Meanwhile, while drives do have a few megabyte of buffer (typically 16 or 
32 MB), typical to-platter transfer rates run perhaps a quarter of that 
(100 MByte/sec is quite good).

So you should EASILY be able to double-up on the "spinning rust" drives 
on USB 3 and still have plenty of bandwidth to spare, tho SATA 2 was 
indeed a bottleneck.  If you're running a fast SSD, a dedicated USB 3 
port will bottleneck on it compared to SATA 3, but not horribly so, and 
it will still be MUCH faster than spinning rust.

Meanwhile, wikipedia's device bitrate table[1], from which I got the 
above, also lists audio bitrates.  CDA: 1.411 Mbit/sec.  S/PDIF: 3.072 
Mbit/sec, AC'97 12.288 MBit/sec.  Even full-rate HDMI audio should be no 
problem, at 36.864 Mbit/sec.  Even USB 2 (480 Mbit/sec) should have 
absolutely no problem with that, which is why USB sound cards are viable 
and there's even some reasonably high end versions.

Uncompressed video, OTOH, could be a bit of a different story.  HDMI 1.0 
and single-link DVI are both 4.95 Gbit/sec, so will stress USB 3 and 
SSDs.  Full-speed dual-link DVI is 8.03 Gbit/sec, and HDMI 1.3 is 10.2 
Gbit/sec, which will challenge any consumer-level storage today.  PCIE of 
sufficient version and/or X can handle it (thus the common 16X PCIE 
graphics cards), but you'll be paying a pretty penny for storage of any 
significant size that can keep up!

Which of course is why pretty much all video of significant resolution 
and frame-rate is also significantly compressed -- it's pretty much 
unmanageable, storage-wise, otherwise.  But it doesn't sound like you're 
doing that heavy video or you'd not be worried about sound at all.


Meanwhile, there's the whole "will it boot" question.  However, as 
someone else mentioned, MS Windows 8 almost certainly means UEFI, which 
should be pretty flexible, provided of course that you're not running the 
MS side too locked down (MS requires that UEFI be user unlockable on amd64 
for certification, so you should be able to unlock it).

But beware, there are some USB drives that won't boot, at least not on 
BIOS (I'm not sure about UEFI).  One way around that is to stick grub or 
whatever, along with the kernel (so basically your /boot) on a bootable 
thumbdrive (which you can stick in a USB 2 slot since for just grub speed 
isn't a huge issue) and boot it, then point the kernel at the otherwise 
unbootable USB drive for root, since the kernel should be able to handle 
even otherwise unbootable drives, once it's loaded.  That's what I'm 
doing here with my external-drive level of bootable system backup, since 
the drive isn't otherwise bootable.

---
[1] https://en.wikipedia.org/wiki/List_of_device_bit_rates

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
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