[Discuss] RAID question

[Patrick]

On Sun, 1 May 2016 04:08:00 -0700
Murray Strome wrote:

[...]
> >
> Have you thought of setting up your drives as ZFS?

Whoah...  That *is* pretty cool.  I need to read more about this,
but here's a few first impressions...

From;
    https://en.wikipedia.org/wiki/ZFS#Native_ZFS_on_Linux

    Ubuntu 16.04 LTS (Xenial Xerus) has ZFS built in by
    default. In Gentoo, configuring a ZFS root filesystem
    is well documented and the required packages can be
    installed from its package repository. Slackware also
    provides documentation on supporting ZFS, both as a
    kernel module and when built into the kernel.

Ubuntu 16.04...  Looks like you picked the exact right time to
mention this.  ;-)

I'd been skeptical of software RAID, and as such hadn't paid much
attention to it -- not nearly enough attention, from the looks of
this.  :-\  But I was really impressed with the *hardware* RAID
in this server I got cheap a while ago [and if you're wondering
why I'd want to keep a piece of industrial hardware as a pet, you
don't know me very well...  ;-)  It actually has come in handy
for video editing, btw].  Yanked two random drives out of it and
kept watching YouTube videos, but pulling a third [out of six]
crashed it.  No prob; putting that last drive back where I'd
found it restored normal function.  Putting the other two back,
in *reverse_order*, also did no lasting harm.  The array healed
itself [indicated by disk-access lights continually flickering
for the next few hours].

Software RAID seemed to dump a lot of that work on the user, but
ZFS looks competent enough to take care of itself, for the most
part.  The fact that your file server's installed on an old
computer also suggests that ZFS is quite low-overhead.  That was
my other main concern about software RAID; it seemed to dump a
hardware job on the software, with all the usual performance
penalties.  When software tries to emulate hardware, it always
slows things down by some fraction.

> I have set up a FreeNAS Network Attached Storage system with 5 hard drives as RAIDZ2 which means that the files can be recovered if any two drives fail. Although none of the drives themselves have yet failed, I had some SATA cable issues that caused problems equivalent to two disks failing, and once I replaced the cables causing problems, all the data was recovered automatically.

Do you know where to find info on physical drive capacities vs
virtual drive capacity in RAID Z# arrays?  I imagine as a general
rule of thumb, greater safety = reduced capacity, while greater
redundancy = better performance.  And as with traditional RAID,
I'm guessing the more physical drives you have in an array, the
better it performs.  But I haven't found any hard numbers.

> I built this using an old computer, and it seems to be working very well now. The FreeNAS OS is based upon Open BSD. In my case, it is on two 16GB USB drives (mirrored) so if (or should I say when, since it is inevitable) one fails, the system will still be operational, and the faulty one could be easily replaced.
> There is a free training webinar available from FreeNAS.org which is repeated every weekday at 10:00AM PDT and which is updated frequently.
> 
> http://www.freenas.org/freenas-zfs-training/
> 
> Although you may not be interested in setting up a Network Attached Storage Server, a lot of the session is devoted to explaining ZFS and RAIDZ, so you might find it interesting.

Not sure if I'd set up a central server; I still favour FTP for
moving stuff around the house [LAN], with a server and/or client
installed on each machine.  Very OS-agnostic; you can find an FTP
client for *any* system.  I even have one on my old Mac, which
turned 20 last Nov.  :-)

But as a really *safe* filesystem, with a few semi-autonomous
maintenance tools thrown in for good measure, this looks great.
It's not useful for this particular project, but will definitely
come in handy.  Thanks!  :-)


> 
> Murray

Patrick.
-- 
"The most fatal blow to progress is slavery of the intellect. The
 most sacred right of humanity is the right to think, and next to
 the right to think is the right to express that thought without
 fear."
		-- Helen H. Gardner, 'Men, Women and Gods'