Re: [gentoo-user] Hard drive storage questions

[Rich Freeman]

On Thu, Nov 8, 2018 at 8:16 PM Dale <rdalek1967@×××××.com> wrote:
>
> I'm trying to come up with a
> plan that allows me to grow easier and without having to worry about
> running out of motherboard based ports.
>

So, this is an issue I've been changing my mind on over the years.
There are a few common approaches:

* Find ways to cram a lot of drives on one host
* Use a patchwork of NAS devices or improvised hosts sharing over
samba/nfs/etc and end up with a mess of mount points.
* Use a distributed FS

Right now I'm mainly using the first approach, and I'm trying to move
to the last.  The middle option has never appealed to me.

So, to do more of what you're doing in the most efficient way
possible, I recommend finding used LSI HBA cards.  These have mini-SAS
ports on them, and one of these can be attached to a breakout cable
that gets you 4 SATA ports.  I just picked up two of these for $20
each on ebay (used) and they have 4 mini-SAS ports each, which is
capacity for 16 SATA drives per card.  Typically these have 4x or
larger PCIe interfaces, so you'll need a large slot, or one with a
cutout.  You'd have to do the math but I suspect that if the card+MB
supports PCIe 3.0 you're not losing much if you cram it into a smaller
slot.  If most of the drives are idle most of the time then that also
demands less bandwidth.  16 fully busy hard drives obviously can put
out a lot of data if reading sequentially.

You can of course get more consumer-oriented SATA cards, but you're
lucky to get 2-4 SATA ports on a card that runs you $30.  The mini-SAS
HBAs get you a LOT more drives per PCIe slot, and your PCIe slots are
you main limiting factor assuming you have power and case space.

Oh, and those HBA cards need to be flashed into "IT" mode - they're
often sold this way, but if they support RAID you want to flash the IT
firmware that just makes them into a bunch of standalone SATA slots.
This is usually a PITA that involves DOS or whatever, but I have
noticed some of the software needed in the Gentoo repo.

If you go that route it is just like having a ton of SATA ports in
your system - they just show up as sda...sdz and so on (no idea where
it goes after that).  Software-wise you just keep doing what you're
already doing (though you should be seriously considering
mdadm/zfs/btrfs/whatever at that point).

That is the more traditional route.

Now let me talk about distributed filesystems, which is the more
scalable approach.  I'm getting tired of being limited by SATA ports,
and cases, and such.  I'm also frustrated with some of zfs's
inflexibility around removing drives.  These are constraints that make
upgrading painful, and often inefficient.  Distributed filesystems
offer a different solution.

A distributed filesystem spreads its storage across many hosts, with
an arbitrary number of drives per host (more or less).  So, you can
add more hosts, add more drives to a host, and so on.  That means
you're never forced to try to find a way to cram a few more drives in
one host.  The resulting filesystem appears as one gigantic filesystem
(unless you want to split it up), which means no mess of nfs
mountpoints and so on, and all the other headaches of nfs.  Just as
with RAID these support redundancy, except now you can lose entire
hosts without issue.  With many you can even tell it which
PDU/rack/whatever each host is plugged into, and it will make sure you
can lose all the hosts in one rack.  You can also mount the filesystem
on as many hosts as you want at the same time.

They do tend to be a bit more complex.  The big players can scale VERY
large - thousands of drives easily.  Everything seems to be moving
towards Ceph/CephFS.  If you were hosting a datacenter full of
VMs/containers/etc I'd be telling you to host it on Ceph.  However,
for small scale (which you definitely are right now), I'm not thrilled
with it.  Due to the way it allocates data (hash-based) anytime
anything changes you end up having to move all the data around in the
cluster, and all the reports I've read suggests it doesn't perform all
that great if you only have a few nodes.  Ceph storage nodes are also
RAM-hungry, and I want to run these on ARM to save power, and few ARM
boards have that kind of RAM, and they're very expensive.

Personally I'm working on deploying a cluster of a few nodes running
LizardFS, which is basically a fork/derivative of MooseFS.  While it
won't scale nearly as well, below 100 nodes should be fine, and in
particular it sounds like it works fairly well with only a few nodes.
It has its pros and cons, but for my needs it should be sufficient.
It also isn't RAM-hungry.  I'm going to be testing it on some
RockPro64s, with the LSI HBAs.

I did note that Gentoo lacks a LizardFS client.  I suspect I'll be
looking to fix that - I'm sure the moosefs ebuild would be a good
starting point.  I'm probably going to be a whimp and run the storage
nodes on Ubuntu or whatever upstream targets - they're basically
appliances as far as I'm concerned.

So, those are the two routes I'd recommend.  Just get yourself an HBA
if you only want a few more drives.  If you see your needs expanding
then consider a distributed filesystem.  The advantage of the latter
is that you can keep expanding it however you want with additional
drives/nodes/whatever.  If you're going over 20 nodes I'd use Ceph for
sure - IMO that seems to be the future of this space.

-- 
Rich