Bananian

SATA port multiplier support

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tkaiser  
Edited by tkaiser at Fri Dec 19, 2014 10:55
ExRaspberry replied at Wed Dec 17, 2014 19:06
that's why I wanted to create a RAID1. All my personal data might get inrecoverable lost if there's no backup


Do you really confuse RAID-1 with backup?

What else would you need to use RAID1 for?

tkaiser  
RAID-1 is the idea to get more reliability/availability ("business continuity") due to added redundancy or the elimination of so called 'single points of failure' (SPoF).

The idea is that the loss of a disk doesn't mean service disruption (maybe you already get an idea that you need 'business critical' services to get something useful out of this RAID-1 thing). It has nothing to do with data safety since it's just added redundancy (everything that gets corrupted/deleted on one disk is broken on the other instantly as well).

If you care about data safety and your 'business' is non-critical regarding service disruptions then get a second Banana Pi, a hard disk with the capacity of 125%-150% of your real data, set them up on different locations in your flat/house and run rbackup or something similar between them to do real backup (and this means that versioning is involved: something that changes on the source location won't automatically be changed on the target but preserved instead to serve for restore purposes).

And while RAID-1 might work with el Cheapo NAS devices that use reasonable hardware even with ARM (Marvell Kirkwood/Armada) it's simply not possible to achieve the design goals of RAID-1 on the BananaPi with crappy Port Multipliers. The same applies to 'higher' RAID levels as well especially RAID-5 which shouldn't be used since years since it's failure prone by design given the capacity and error rates of the hard disks we use these days.

You're right. Safety is the wrong term. I'm just scared of an HDD that becomes unreadable in case of an hardware issue.
Do you see any chance to achieve this by a single Banana Pi?

I've been running a simple NAS on my old Raspberry Pi. but I'm always scared of a drive blackout. When I heared that the Banana is able to use multiple sATA drives by with an PM I thought this would be the perfect solution for me.

A real server is way oversized. I'm using my NAS for sharing all my music and videos for all my devices, as well as a VPN server by dyndns.
I thought of buying a cheap dedicated NAS which might have 2 or 4 slots for harddrives. But then I found the Banana - which in comparison to my Raspberry runs like a rabbit...

tkaiser  
Edited by tkaiser at Sun Dec 28, 2014 03:28
ExRaspberry replied at Fri Dec 26, 2014 19:18
I'm just scared of an HDD that becomes unreadable in case of an hardware issue.


Then do backup. It's that simple and also helps against the main reasons why backups exist: human or software misbehaviour.

I've seen so many cheap RAID setups failing when you need them, I've seen a couple of 'great' data losses due to a misunderstanding of redundancy that I took it as a simple rule: Always backup first. Then you can play around with redundancy to enhance availability in case of hardware failures. But you won't loose all your data when your RAID breaks.

Edited by ExRaspberry at Tue Dec 30, 2014 23:49

Any idea how to create automatic backups on different disks using a single Banana pi?
I thought using OMV would be a great idea - especially as I didn't create backups the last years...

tkaiser  
Edited by tkaiser at Wed Dec 31, 2014 01:34
ExRaspberry replied at Tue Dec 30, 2014 23:36
Any idea how to create automatic backups on different disks using a single Banana pi?


I received a cheap JMB321 based Port Multiplier but hadn't the time to play around with it ('playing' means testing worst case scenarios). If a PM will work reliably in situations with high I/O load then you could simply use something like rsnapshot http://www.rsnapshot.org to automate the task.

Since it's essential to store backups in a different location than the data itself I would go with a second Banana Pi and a larger hard disk (the Seagate Archive HDDs provide an excellent price/capacity ratio) and would do rsnapshot through the network afterwards. But since we're working in this business and have seen so many failures and data losses (due to simple human mistakes, so called 'bit rotting' and hardware failures) I would never ever store important data on a Banana Pi or cheap low end NAS devices. But that's based on personal experience

So you didn't gain any experience if a Banana Pi using a cheap JMB321 PMP and running OpenMediaVault in Raid1 mode might be a suitable solution for private usage?

I'd like to have two old sATA drives to test that case... but at the moment I only have a 250gb drive spare. Maybe I'll get another one soon to check if the Banana Pi OMV Nas fulfills my needs ;)

If you have the equipment and time to check this, I'd really appreciate your results!

tkaiser  
ExRaspberry replied at Thu Jan 1, 2015 20:28
So you didn't gain any experience if a Banana Pi using a cheap JMB321 PMP and running OpenMediaVault ...

Others did already. Read f4exb's experiences here: http://forum.lemaker.org/thread-9207-1-1.html

The whole idea is crap since combining a couple of really unreliable hardware pieces together can not lead to more realiability. It simply does not work. You might add redundancy. But some that serves no specific purpose since your RAID setup will fail exactly in the moment when you would need it: At rebuild time. And exactly the same applies to many other cheap and crappy NAS/RAID combinations that suffer from reliability. RAID works as long as you don't need it.

My tests regarding Port Multipliers are targeted at another use case: Using a couple of disks in a controlled round robin fashion. But I will test worst case scenarios of course since when this won't work then the whole idea to rely on this sort of hardware is crap. I don't like implementations that only work when boundary conditions are perfect. Since reliable storage has to work under worst case conditions otherwise it's simply the wrong implementation.

BTW: You get really cheap x86 based setups with 4 SATA ports using Celeron J1800/J1900 or AMD's A1. But I wouldn't do RAID on such more reliable setups as well. Since I've seen so many RAIDs failing, dealing with bit rotting due to faulty RAM and so on. I would go at least with a N54L, ECC-RAM and double redundancy if the data to be stored has any value and I would need RAID (once again: RAID has nothing to do with data safety but just with availability)

It is not an issue to run NAS on low cost configuration (without RAID and ECC RAM) as long as you use ZFS for example. There are freely available NAS system distributions which use ZFS as a foundation. Please look at www.freenas.org

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