Hardware Raid1

[Chris1969]

I stumbeld over this hardware RAID system: Raidon We-Ra. SATAIII/SSD in IR2022

Can I use my gentoo system with such a hardware RAID? Are there any points I should consider.

[NeddySeagoon]

Chris1969,

Its a RAID1 system. I wouldn't count on it being hardware though.
If it appears as a single SATA drive, its a black box. You have no idea how the RAID is implemented.

Try it.

[Banana]

Do you have a link to a handbook or description of this device?
I'v found a hardware box with two disk compartments. And you connect it with sata cable.
So if it is really a hardware raid, you should be able to access it from any decive connected to. For a laptop you something which would provide a sata connection.

[Chris1969]

Thanks NeddySeagoon and Banana for your answers!

I only found this (probably I am not supposed to post any pdfs), so here's the link where you can find product sheets of the iR2022 and iR2024: http://www.raidon.com.tw/RAIDON2016/download.php

I wonder if it would work with two different ssd models?
Also with different hard drive capacities?

[NeddySeagoon]

Chris1969,

The HDD models won't matter.
With different drive capacities, RAID1 will be physically limited to the capacity of the smallest drive.
What happens with the wasted space on the larger driver is not specified.

As its an enclosure, it may matter where the small drive goes.

-- edit --

It offers both raid1 and raid0 but I didn't see any mention of JBOD (Just a Bunch of Drives) mode. Now I've read the manual, both modes are restricted by the size of the smallest drive.

[Chris1969]

Thanks NeddySeagoon for sharing your knowledge with me!!

So if I understand/imply correct:

1. I could start using the RAID hardware with only my existing hard drive holding my gentoo system

2. add any other EMPTY harddrive big enough

3. the RAID hardware will duplicate/copy /backup on the second drive

4. if any of the two disk fails, the system runs from the remaining sane disk

5. until I replace the failed one with any disk big enough

6. If desired I could use any of the two disks to boot from outside the RAID hardware again?

[Banana]

1. I could start using the RAID hardware with only my existing hard drive holding my gentoo system

First you are talking about RAID1, right? https://en.wikipedia.org/wiki/Standard_RAID_levels
Second: no. More on that later

2. add any other EMPTY harddrive big enough

Yes

3. the RAID hardware will duplicate/copy /backup on the second drive

Depends on the device. Some do this automatically, some need a command to run.

4. if any of the two disk fails, the system runs from the remaining sane disk

Yes

5. until I replace the failed one with any disk big enough

Yes

6. If desired I could use any of the two disks to boot from outside the RAID hardware again?

No. See below.


This is a very simplified version about what is going on and there are multiple opinions on this:
A RAID (hardware or software) is kind of a abstraction layer which sits "between" the disk and the operation system.
You can not just add a disk as it is to the RAID. It needs to be fromatted. The RAID does handle the disks and presents them to the OS.
So, adding a new disk will erase the data in this disk and reformat it.
Removing the disk from the RAID, will result in a working disk, but you can not easily read the data on it, because this abstraction layer is missing.

On the other hand, if you really have the knowledge and tools, you could revover the data from a disk outside the RAID array.
And it heavily depends on the used hardware.

Long story short, make a backup and try it at first with some spare disks, otherwise you will loose data.

[Chris1969]

Thanks, to you both.

Maybe I will try the RAID1 somewhere in the future, but not in the near one.

I searched a little bit more,

on the question of readability of single disks outside the RAID1, if found this interesting: http://forums.anandtech.com/threads/rai ... ne.293134/

and on the question of boot-ability of single disks, this: http://unix.stackexchange.com/questions ... aid1-array

Regards
Chris

[NeddySeagoon]

Chris1969,

6. The answer is 'maybe'. it depends on the on disk data format, which is not known.

There are several possiblities.
1. It really is hardware raid and it uses a propritary on disk format. The kernel won't understand that, so its a no.
2. It's software 'BIOS' fakeraid. There is a kernel module for that for some fakeraid formats.
3. Its mdadm software raid. The kernel understands that but there are two major varients. One has the raid metadata at the start of the disk, where the first filesystem would start. The other, older format, has t_e raid metadata at the end of the disk, so the kernel can just ignore the raid like it wasn't there.

Long story short. It's unlikely but not impossible.

Hardware raid does nothing for raid levels 0 and 1, so it's unlikely to be hardware raid container. It's just a black box. You have no idea how it works but using the drives outside the box needs that knowledge

To keep your options open, with a raid 1 setup, use kernel software raid.

Raid is not a backup.

Code: Select all

rm very_important_file

removes it from both mirrors. You still need to keep backups.