Re: [gentoo-user] Getting maximum space out of a hard drive

[Frank Steinmetzger]

Am Mon, Aug 29, 2022 at 04:28:55PM -0500 schrieb Dale:

> >> It sort of reminds me of a cell phone.  Small but fast CPUs, some even
> >> have decent amounts of ram so they can handle quite a lot.  Never heard of
> >> this thing before.  I wouldn't mind having one of those to work as my
> >> OpenVPN server thingy.  I'd just need to find one that has 2 ethernet
> >> ports and designed for that sort of task. 
> > Many of the ZBoxes have dual NICs, which is what makes them very popular
> > among server and firewall hackers because they are also very frugal. My
> > particular model is the CI331:
> > https://www.zotac.com/us/product/mini_pcs/zbox-ci331-nano-barebone
> > It has one 2,5″ slot and one undocumented SATA M.2 which can only be reached
> > by breaking the warranty seal. That’s where zotac installs a drive if you
> > buy a zbox with Winblows pre-installed.
> >
> > After updating the BIOS, which allowed the CPU to enter lower C states, it
> > draws 6 W on idle. It’s not a record, but still not so much for a 24/7 x86
> > system.
>
> I was looking for one with two ethernet ports but wasn't having any luck
> yet.  I did find and download like a catalog thing but it will take a
> while to dig through it.  They have a lot of models for different
> purposes.

Here’s a list of barebone systems with dual-nics:
https://skinflint.co.uk/?cat=barepc&xf=19071_2
You can narrow down your criteria in much detail, such as passively cooled¹,
CPU vendor and features (hello, AES) or even if it’s officially suited for
conutinuous operation by the manufacturer. Obviously, mini barebones are not
suited for big NAS duty due to their form factor.

I mentioned this site before. But even though it’s EU centric, many products
are available worldwide (or in regional variants). Others on the list chimed
in and named more sites, but I can’t remember them.

> I did see a pre-made thing on ebay but can't recall the brand that cost
> hundreds that was made just for VPNs and such.

VPN appliances are pricey due to their industrial design. But for a normal
dude like we are, a consumer-grade device might be better suited. Especially
if it can be used for other purposes such as media source for the TV.

> It was really pricey tho.  But, you plug it in, boot it up and it had
> evrything installed and then some to control networks traffic.  It had
> stuff I never heard of. 

Industrial stuff, as I said. And you pay for the bespoke software, without
which the appliance probably won’t work.

> >>>> I have a old computer that I might could use.  It is 4 core something
> >>>> and I think it has 4GBs of memory, maxed out.  I think it will perform
> >>>> well enough but wish it had a little more horses in it.
> >> I'm not real sure what that old machine has.  I have Linux, can't recall
> >> the distro tho, on it.  Is there a way to find out if it supports the
> >> needed things?
> > cat /proc/cpuinfo and look for aes or the like.

> I have booted that old thing up and I grepped cpuinfo and no AES that I
> could see or grep could find.  Must be before it's time. 
>
> While I had it booted up, I checked into what all it did have.  It only
> has 4 SATA ports, one already used for the OS hard drive.  I could
> likely run it from a USB stick which would make all 4 available.  It has
> 8GBs of memory too.  CPU is a AMD Phenom 9750 Quad running at 2.4GHz.  I
> found it add that cpuinfo showed a different speed I think.

cpuinfo shows the current frequency, not the maximum.

> It's not a speedster or anything but I may can do something with it.

According to https://en.wikipedia.org/wiki/List_of_AMD_Phenom_processors the
9750 Quad is a 95 W or 125 W processor. Going by
https://www.cpubenchmark.net/cpu.php?cpu=AMD+Phenom+9750+Quad-Core&id=306
its single-thread power is ca. ⅔ that of the Celeron N5100 on my ZBox (at 6 W):
https://www.cpubenchmark.net/cpu.php?cpu=Intel+Celeron+N5100+%40+1.10GHz&id=4331

> >> I'm pretty sure they support RAID and such by default.  It is likely set
> >> up to make setting it up easier too. 
> > They do, naturally. And yes, the frontends hide lots of the gory details.
>
> That's my thinking since RAID, ZFS and such are new to me.  Of course,
> front ends do take away a lot of fine controls too, usually. 

Setting up ZFS is—from a technical POV—not that much different from LVM,
which you are familiar with. You have block devices over which you create a
virtual device (vdev). A vdev can be a single disk, or a mirror of disks, or
a parity RAID. A storage pool is then created over one or more vdevs. And in
that pool you can create several ZFS (or just the one that is created with
the pool itself).

┌POOL───────────────────────────┐
│┌VDEV 1────┐┌─VDEV 2────────┐ ┌┴ZFS────┐
││  mirror  ││  parity RAID  │ │  /pool │
││┌───┐┌───┐││┌───┐┌───┐┌───┐│ ├─ZFS────┴─────┐
│││sda││sdb││││sdc││sdd││sde││ │  /pool/video │
││└───┘└───┘││└───┘└───┘└───┘│ └┬─────────────┘
│└──────────┘└───────────────┘  │
└───────────────────────────────┘

In comparison:
LVM: block device/partition → physical volume → volume group → logical volume → any file system
ZFS: block device/partition                   → vdev         → pool           → ZFS filesystem

The beauty is that ZFS can take care of everything. You just give it whole
block devices and at the other end you get a mountable file system. What you
also get is protection from bitrot thanks to in-FS checksumming. You don’t
get that with rsync on ext4. That’s why eventually I decided for ZFS for my
NAS over other, perhaps more practical solutions like LVM on mdraid. When it
checks the pool’s integrity, it is faster than mdraid, because it knows
where actual data is stored, so it can skip empty parts.

The biggest disadvantage over LVM is that it’s rather limited regarding
adding or removing disks. You cannot simply add a disk to a parity VDEV,
only to a mirror (which only increases redundancy, not capacity). And once a
new vdev is added to a pool, you cannot remove it, only replace its disks.
People added a single disk to a pool by accident and had to rebuild the
entire thing as a result. (Though I think that particular problem has been
dealt with recently.)

There exist of course some technical pitfalls. The ashift parameter
determines how big the smallest block of data is and should not be smaller
than the HDD’s block size. Hence, ashift=12 (2^12=4096) is the minimum one
should use these days. But I think it’s become the default anyways. Another
is the record size, which is the logical data block size for striping, IIRC.
For bigger files like video, it’s more efficient to use a bigger block size
(say, 1 MiB) than a smaller like 64 k, because it improves the ratio of
metadata over payload.


¹ Regarding passive cooling: I like it, because fans break and make noise.
But running Gentoo on a tiny box with a small heatsink may put too much
stress on the electronics. When I tested out the performance of the ZBox, I
played Warzone 2100—a 3D realtime strategy game—on it on my 2560×1440 screen
(fluently, I might add). But afterwards the whole case was HOT.

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