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Re: RAID levels not intuitive in anaconda GUI

On Dec 19, 2012, at 2:39 PM, Máirín Duffy <duffy fedoraproject org> wrote:

> On 12/19/2012 04:26 PM, Marian Ganisin wrote:
>> On this screenshot (attached to original bug):
>> https://bugzilla.redhat.com/attachment.cgi?id=640017
>> First checkbox has label 'Redundancy', last checkbox has label 'Redundant'. In my understanding same terms. Additonally they aren't different by any means, just two equivalent checkboxes for 'redundancy' in same group.
>> Btw that 'RAID6' label visible on the screenshot does not bring any light to selected configuration.
> They're not in the same group. The first checkbox you're referring to is
> the Redundancy checkbox for data redundancy. The second one, you'll note
> in the screenshot, is indented under the 'Error detection (partity)'
> checkbox. It is a child of the error detection checkbox, and means
> redundant error detection / partity, not redundant data.
> I'm sorry that the two similar words confused you. Maybe we can indent
> the parity options a bit more so it's clearer they apply to error
> detection, or grey them out unless error detection is selected.

There are some problems with this UI that I mentioned in August, primarily related to Btrfs. I didn't revisit this RAID UI after the extra options that don't apply to Btrfs were removed.

Currently the UI implies at first glance that a lot of RAID and nested RAID levels are supported because of the use of only checkboxes and no graying:  RAID linear, 0, 1, 4, 5, 6, and also nested 01/10, 04/40, 41, 05/50, 51, 06/60, 61 are implied, with associated ambiguity on which nesting order is used. And I have to ask if any nested RAID other than 10 is seriously going to be supported for installs. It seems excessive to me.

Anyway, for someone who understands RAID I find the UI intensely confusing as to what I'm going to get, even setting aside the RAID level label in 18.37.4-1 always says RAID0 no matter what is chosen.

1. I suggest exchanging "Redundancy (mirror)" for "Mirroring". Redundancy applies to RAID 1, 4, 5, 6 so using it as a primary term is confusing. If this checkbox means RAID 1, then it really ought to say just "Mirroring" or "Mirroring (RAID1)".

2. "Optimize performance (stripe)" I think it's more clear if this "Performance optimized striping" if this is meant just for RAID 0.

3. "Error detection (parity)" is a confusing label. Parity applies to md RAID 4, 5 and 6 and I can check this option by itself with nothing else checked which then implies RAID 4 which is so uncommon that supporting it doesn't make sense. Once selected I can't deselect it; and I can't select either option below. But I can select the two options above. So upon checking this, I have RAID 4, and can choose either RAID 41 or RAID 40, which are even more rare than RAID 4.

Error detection itself is misleading because in normal operation RAID 4, 5, 6 themselves do not detect any errors above what the drive firmware detects (which is the same for RAID 1 and RAID 0). In order to get error detection the user must initiate or schedule a scrub or repair. Conversely, Btrfs does have error detection which is active during normal operation regardless of the profile used.

Error correction is true, but it's also true for RAID 1.

4. "Distributed" parity applies to RAID 5 or 6. It's unclear which I'll get, or why I can select it all by itself with no other options including without Error detection (parity) selected.

5. "Redundant" under Error detection is confusing. RAID 4 is redundant, RAID 5 is redundant, RAID 6 is redundant. I'd guess it means RAID 6 except…

6. I can't choose both Distributed and Redundant, also very confusing, so Redundant must not mean RAID 6.

Items 3-6 I think need to be consolidated into just RAID 5 or 6, and skip RAID 4. As for what plain language to use to describe them, it's difficult. "Single drive fault tolerance" is maybe OK, but that applies to a two disk RAID 1.

And possibly the best multidisk options, which are also the easiest and fastest to grow when more space is needed: linear, and RAID 1+linear, combined with XFS for parallelization. But this isn't an option at all.

Chris Murphy

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