Re: Hardware for a back up server? [WAS Re: How to use dmsetuup?]
On Sat, Nov 11, 2023 at 04:01:47PM -0800, David Christensen wrote:
> On 11/11/23 08:52, Andrew M.A. Cater wrote:
> > On Fri, Nov 10, 2023 at 10:22:07PM -0500, gene heskett wrote:
> > > On 11/10/23 19:46, David Christensen wrote:
> > > > On 11/8/23 02:20, gene heskett wrote:
> >
> > Are these 2TB SSDs or hard disks? I would counsel very strongly indeed
> > against using any ARM-based single board computer as a RAID device on
> > USB connections - they're just *not* up to it.
>
This at least partly because the USB devices on, say, a Raspberry Pi
tend to share I/O and resources. On a Pi, USB3 takes away from the
Ethernet, for example.
>
> On 11/11/23 09:05, Stefan Monnier wrote:
> > I don't think the issue is whether they're ARM based.
> >
> > The issue is simply how you connect the disks: in my experience, disks
> > connected via USB are simply not quite up to a 24/7 situation,
> > especially if the disk is USB-powered.
>
Right.
>
> >
> > I have 4 SSD drives connected to a single RPI4 currently, using a
> > powered USB hub.
> >
SSD significantly different to HDD.
>
>
> On 11/11/23 10:47, Stefan Monnier wrote:
> > Hmm... so maybe the USB connection is not directly relevant either
> > and the real issue is the power?
>
>
> An obvious difference between internal and external drives is physical
> protection. Internal drives and cables are protected. Everything gets
> power from the same source (PSU, PCU fed by dual PSU, etc.). External
> drives, cables, and power adapters can be moved, yanked, disconnected,
> dropped, kicked, subjected to electrostatic discharge, etc.. There are more
> parts to fail and more opportunities for failure with external drives than
> with internal drives.
>
This is what I meant: this is why the devices from QNAP / Synology that
are plug and play NAS are also built this way. The Synology devices
can take lots of added modules, seemingly - it all seems expensive
but these are designed for plugging in and the whole thing "just working".
>
> It is not uncommon for communications establishment to fail with external
> drives. Similarly, communications re-establishment when the computer and/or
> drive resume from a power saving mode. Writing and testing this kind of
> software is difficult and you need people with both both CS and EE skills.
> There is an astronomical number of combinations to design and test for. The
> code runs rarely. For reliable 24x365 operations, the challenge is
> eliminating everything that can cause communications establishment/
> re-establishment -- operator steps, computer configuration, drive
> configuration, power failures, cooling failures, etc.. If you can find and
> eliminate all of them, a USB external drive can stay connected a very long
> time.
>
*If* is very much the word, I think.
>
>
> I have always liked ATX tower cases with lots of drive bays, both internal
> and external. Over time, more products have become available with good
> cooling and low noise. I have not found a major computer manufacturer who
> makes servers with all of those features, so I build my own:
>
> * Fractal Design Define R5 case
> * 3 @ Fractal Design low-speed 140 mm fans
> * Fractal Design Ion+ 2 Platinum 660 W power supply
> * Intel S1200V3RP motherboard
> * Intel Xeon E3-1200 v3 series processors
> * Dual channel ECC memory
> * LSI 9207-8i HBA with "IT mode" non-RAID firmware
> * Seagate Barracuda and Constellation ES.2 HDD's
> * Intel 520 Series SSD's
> * StarTech 2.5" and 3.5" mobile racks
> * Cable Matters black SATA 6 Gbps cables with locking connectors
>
>
> They are not cheap, small, or light, but they perform well, are easy to work
> on, are reasonably quiet, and everything stays cool. They have plenty of
> capacity for future upgrades.
>
Nice parts list and good suggestions.
>
>
> SSD RAID10 is very impressive when everything else matches. Backups over a
> Gigabit LAN onto SATA III SSD RAID10 does not make sense because Gigabit
> Ethernet is rated for 1 Gbps read/ write and a SATA III SSD RAID10 is rated
> for 24 Gbps read and 12 Gbps write. I would put HDD's in the backup server
> and put the SSD's in the workstation.
>
>
> David
>
there's no doubt that you can do the same with some ARM boards - maybe
the RockPro which has PCIe?? but not with the majority.
Anyway, let's leave folks to build what works for them: the one thing
I've learned from much of this list is that we're all unique in our
requirements, even if we have much in common.
All the very best, as ever,
Andy
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