On Tue, 18 Jul 2006, Dave Howorth wrote:
HG wrote:
Hi!
I'm planning to build a home made NAS using old harware and SUSE. SUSE might not be the best OS for this, but it's the only Linux I have administered at least somewhat.
Ok, what I'm thinking is a old PC with lot's of old disks inside and a gigabit ethernet (planning to do video editing over it also).
Even gigabit ethernet is WAY slower than local disks. You may find it a pain for video editing. It might be OK to store video there, copy it to a local disk while you edit it and then copy it back. But the bottom line is experience - I suggest you set up the gigabit link and run some tests with it first :)
Do you mean to say that gigabit ethernet has less bandwidth than local
disks or that the latency of gig-e is higher? Unless you have some
pretty beefy local disks, gig-e has rather more bandwidth than most
local disks. As for latency, that's not something I can answer, but the
track-to-track on most disks these days is something like 8 ms (right?),
which my local network easily beats. What is the round-trip-time on
something like NFS versus local disks?
I'm not flat-out saying you are wrong, but I'd like you to qualify your
statements and help me understand exactly what you are saying.
As an example, in a situation involving fast ethernet (not gig-e) and
some mid-grade machines (just shy of 1GHz and basic consumer-grade IDE
disks) my local disks top out around 11.45 MB/s (hdparm -t), averaging
8.9 MB/s (dd if=/dev/hda of=/dev/null bs=4k count=10000). Contrast that
with a recent test I performed using ATA over Ethernet, where the disks
were a raid5 on a similar machine but faster disks (about 20MB/s local
read speed on the backing store for the ata-over-ethernet block device)
- the exact same client was able to sustain 11MB/s and with less load,
and not-very-good ethernet cards. By this quick test, and measuring
"bandwidth", ata-over-ethernet was just as fast as, and sometimes faster
than, my local disks. (Granted, not the best test components or the best
test, but it serves to illustrate.) With gig-e one could easily exceed
my local disk speed on a regular basis.
Question: what might be the best way to calculate "latency" in a way
that could be used to compare (for example) ATA-Over-Ethernet to a Local
Disk (both are block devices to the client).
--
Carpe diem - Seize the day.
Carp in denim - There's a fish in my pants!
Jon Nelson