[ale] They say drives fail in pairs...

[Michael Trausch]

On 01/03/2012 04:52 PM, Lightner, Jeff wrote:
> That confuses me.  Does ZFS have built in redundancy of some sort
> that would obviate the need for the underlying storage to be hardware
> RAID?  Or are you saying you'd use ZFS rather than Software RAID?

Both ZFS and btrfs have redundancy capabilities built-in that
(allegedly!) play nicely with the filesystem's built-in dynamic resizing
volume management stuff.  Neither filesystem is "just" a filesystem, but
aims to be a whole volume-management stack.  No more need for things
like LVM, when all you need to do is create an fs on a single whole
drive (no partition table) and hot-add or hot-remove it from the pool of
storage.

The other nifty thing is that they can do redundant data storage on even
a single device, as I understand it, so that you can do things like have
the same data on a single drive in multiple locations, which helps if
one area of the drive goes bad.

I don't use hardware RAID for anything (and I'm not likely to ever do
so).  If I ever needed storage that went beyond what a few hard disks
could provide, or something that needed to be larger than what I would
trust something like ZFS or btrfs to do on their own, I would probably
build a dedicated rack-mount box that had tens of drives in it and use
something like RAID 10 with three stripes.

There was a "DIY" guide to building such a box, along with lists of
hardware and tools needed to build the things, and claiming something
like 100+ TB of storage in a single box.  They're expensive in absolute
dollars, but relatively inexpensive compared to other solutions that
scale that far up in storage space, and they are powered by Linux
software RAID (AFAIK).  You would use the things such that you could
replace standalone failed drives off-line, and replace whole units in
(ideally) only as long as it takes to power one down and install a new one.

I'm not anywhere near that, yet, though.  I can only really forsee
needing to grow to about 6 TB of reliable storage in the next two years,
but given the high rates of change in everything around me at the
moment, I can't really look much farther than that.

	--- Mike

-- 
A man who reasons deliberately, manages it better after studying Logic
than he could before, if he is sincere about it and has common sense.
                                   --- Carveth Read, “Logic”

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