Subject: Re: [bug#64259] [PATCH 2/2] Provide md-array-device-mapping to start MD arrays via UUID or name.

From: Felix Lechner <[email-masked]>
Date: Sun, 22 Oct 2023 10:44:13 -0700

Hi,

Thanks for looking at my patch!

On Fri, Oct 20 2023, Ludovic Courtès wrote:

> Could ... the device names specified in
> the ‘source’ field of the mapped device become invalid?

In RAID failures, the devices for defective components usually stop
functioning as intended or become unavailable altogether. Listing those
devices on the mdadm command line, however, requires them to be present
for the assembly of the array. For the fault-tolerant behavior people
expect, arrays should be started via the array name or the special UUID.

> try and use ‘define-deprecated’.

Yes, thank you! I will do so and deploy locally before I update the
patch herein.

> Instead of “see Mdadm documentation”, could you add a link or a command
> to type to access said documentation?

Upon review, I am not sure that the mdadm documentation is actually very
helpful. I must have been thinking about third-party sites.

> Better yet, an example of what an
> mdadm device name or UUID is and how to obtain it would be welcome.

Yes, I will include examples on how to access both, and how to change
the "array name." The latter can be a chosen string that is optionally
prefaced by the local host name. The array name is not the same as the
device name, which looks like /dev/md12. I shall clarify all that in the
revised patch.

>> +    (if (and array-selector md-device)
>            ^
> This condition is always true.

Okay, I may not know Guile macros well enough.

> Instead of renaming and duplicating part of the logic, how about
> supporting those new ‘source’ specification right in ‘open-raid-device’?
> It would emit a deprecation warning when ‘source’ is a list of strings.

It's an good idea, but many other file systems offer RAID-type
functionality. Do you think that a raid-device-mapping based on mdadm
occupies a fair share in the common name space?

> Does the busy wait loop currently in ‘open-raid-device’ need to be
> preserved?

I personally do not believe so but I'll defer to Andreas Enge, whom I
copied on this message. I believe Andreas wrote the original device
mapping.

Kind regards
Felix