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Re: [tlug] White Box: Some Assembly Required ...

Hi CL,

here's my word of advice regarding RAID5 and long term storage.
I used to work, among other things, as a system and network admin for a large Institution,
so before the advent of large scale virtualization we used to have a great number of servers
set up with RAID 5 , RAID 6 and hybrid schemes such as RAID 5 plus hot spares.

When you read "very high fault tolerance" in a certain RAID scheme, please take note this fault tolerance only refers to physical disk failures.

In case one or two (depending on the scheme) of your disks do fail, your data is still safe.

BUT, no RAID will protect you from:

- filesystem-level corruption. That cannot be prevented by RAID schemes.
- logical corruption within the array itself. If your controller for any reason is malfunctioning.
you may not notice it until your striping / parity data is too damaged for any reconstruction attempt. Also, parity inconsistency caused by system failures can be as bad. Been there, seen that.
- failure of the RAID controller itself. Yeah, that can be a single point of failure, and a very bad one. One does not simply swap in a new RAID controller.
- failure of two (in case of RAID5) or more (in case of RAID6) disks within a short period of time.

Any of the the above can hurt really bad, it can happen, and has already happened many times. Please set up another kind of alternative or offline backup. RAID 5 is mostly about performance and some disk fault tolerance.
Don't use it for long term storage, it's not safe. Any striping / distributed parity scheme will effectively prevent you from recovering your data by most offline means.

If you want something a bit more reliable, that will allow you to recover your data in case your controller fails, at least use mirroring. If possible, mirror to more disks, not just 1:1. I would rather setup a rsync job that does the trick during the night.
Avoid using any kind of striping, that would be really bad.

Also, disks of the same production lot of just from the same manufacturer have an eerie tendency to fail reliably in the same manner. Again, you don't want to lose two disks within hours, even if you do pure mirroring.

That's it.



On Fri, Jun 22, 2018 at 4:39 PM, CL <> wrote:
Got a bit of a head scratcher going on and, now that I have read
everything I can find on the subject, I feel as though I know less now
than when I started.  I am building / rebuilding a torrenting box.  I
have the following parts, but don't know how to put it all together ...
or whether I can ... to get the setup I think I want.  Can anyone
suggest a possible working setup.  I am not sure I have all of the
software required or that I have hardware bits connected to the right
other hardware.

O/S is Lubuntu 18.04.  No RAID or LVM drivers are installed.

The hardware is:

- ASUS Motherboard (8-core AMD 8370e) with AMD SB950 chipset, which
permits setting up hardware RAIDs (0, 1, 5, 10) and six onboard SATA3
slots. BIOS is the latest version.

- SATA control is set to RAID in BIOS, but that does not seem to have
any effect in the current setup.

- A Kuroto Shikou 10-port SATA3 controller card which is mounted in the
second PCIe x16 slot (x4) (and which reports it is AHCI


- My boot disk is a 120Gb Samsung SSD

- Optiarc CD/DVD R/W

- Six Toshiba 3Tb HDDs, which I want to use to make a hardware RAID 5
long-term storage disk.

- A 2.5 and a 4Tb for current incoming and pre-sorting (and because I
had them and they're free extra storage on which I can place stuff I
want to review immediately or soon before placing in "deep" storage).

What I want to do is have my O/S on the SSD, receive incoming data on
the two "other disks" and organize, sort and catalogue data to be
logically stored on the RAID.

Right now, I have the CD/DVD, SSD, 2.5Tb and 4.0Tb connected to
motherboard slots and I have the six HDDs I want to use for the RAID
connected to the controller card.


When I boot up, I can only see two of the controller card mounted HDDs. 
I've tried switching the cables around and I have two ten-packs of SATA3
cables that I've switched in and out with no change.  I can remove all
of the 3Tb RAID HDDs and start / view them individually in Lubuntu when
they're mounted in a USB chassis.  I have changed cables around and can
always see two, but not always the same two.

In the course of researching the problem, and before I sent this, I
found an AMD report on the SB950 chipset which says that it can only be
used for hardware RAIDs of four disks or less, which means that I should
be trying to make a software RAID from the six HDDs.

The Windows solution is to plug all HDD and SSDs into the controller
card and to start all operations from the card rather than the
motherboard (which seems to me to be creating an electron bottleneck). 
Is that also the Ubuntu solution?

Does RAID / LVM software play a role that I haven't understood or
figured out until now?

I feel as though the answer is staring me in the face, but I am not
seeing it.


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