[RFC PATCH] Detail: don't display the raid level when it's inactive

[RFC PATCH] Detail: don't display the raid level when it's inactive

[Lidong Zhong]

Sometimes the raid level in the output of `mdadm -D /dev/mdX` is
misleading when the array is in inactive state. Here is a testcase for
introduction.
1\ creating a raid1 device with two disks. Specify a different hostname
rather than the real one for later verfication.

node1:~ # mdadm --create /dev/md0 --homehost TESTARRAY -o -l 1 -n 2 /dev/sdb
/dev/sdc
2\ remove one of the devices and reboot
3\ show the detail of raid1 device

node1:~ # mdadm -D /dev/md127
/dev/md127:
        Version : 1.2
     Raid Level : raid0
  Total Devices : 1
    Persistence : Superblock is persistent
          State : inactive
Working Devices : 1

You can see that the "Raid Level" in /dev/md127 is raid0 now.
After step 2\ is done, the degraded raid1 device is recognized
as a "foreign" array in 64-md-raid-assembly.rules. And thus the
timer to activate the raid1 device is not triggered. The array
level returned from GET_ARRAY_INFO ioctl is 0. And the string
shown for "Raid Level" is
str = map_num(pers, array.level);
And the definition of pers is
mapping_t pers[] = {
{ "linear", LEVEL_LINEAR},
{ "raid0", 0},
{ "0", 0}
...
So the misleading "raid0" is shown in this testcase. I think maybe
the "Raid Level" item shouldn't be displayed any more for the inactive
array.

Signed-off-by: Lidong Zhong <lidong.zhong@suse.com>
---
 Detail.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Detail.c b/Detail.c
index 24eeba0..9ac49e5 100644
--- a/Detail.c
+++ b/Detail.c
@@ -427,7 +427,7 @@ int Detail(char *dev, struct context *c)
 			printf("     Creation Time : %.24s\n", ctime(&atime));
 		if (is_container)
 			str = "container";
-		if (str)
+		if (str && !inactive)
 			printf("        Raid Level : %s\n", str);
 		if (larray_size)
 			printf("        Array Size : %llu%s\n",
-- 
2.26.1

Re: [RFC PATCH] Detail: don't display the raid level when it's inactive

[Ian Pilcher]

On 8/26/20 10:16 AM, Lidong Zhong wrote:
> ...
> So the misleading "raid0" is shown in this testcase. I think maybe
> the "Raid Level" item shouldn't be displayed any more for the inactive
> array.

As a system administrator, I'd much rather see "unknown" (or something
similar), rather than simply omitting the information.

-- 
========================================================================
                  In Soviet Russia, Google searches you!
========================================================================

Re: [RFC PATCH] Detail: don't display the raid level when it's inactive

[Zhong Lidong]

On 8/29/20 12:38 AM, Ian Pilcher wrote:
> On 8/26/20 10:16 AM, Lidong Zhong wrote:
>> ...
>> So the misleading "raid0" is shown in this testcase. I think maybe
>> the "Raid Level" item shouldn't be displayed any more for the inactive
>> array.
> 
> As a system administrator, I'd much rather see "unknown" (or something
> similar), rather than simply omitting the information.
> 
Thanks for the suggestion.
Yeah, just removing the Raid Level info is not the best option. I also
considered to show it as "inactive Raid1" in such case. Anyway, I need
to wait for Jes's review.

Re: [RFC PATCH] Detail: don't display the raid level when it's inactive

[Nix]

On 31 Aug 2020, Zhong Lidong told this:

> On 8/29/20 12:38 AM, Ian Pilcher wrote:
>> On 8/26/20 10:16 AM, Lidong Zhong wrote:
>>> ...
>>> So the misleading "raid0" is shown in this testcase. I think maybe
>>> the "Raid Level" item shouldn't be displayed any more for the inactive
>>> array.
>> 
>> As a system administrator, I'd much rather see "unknown" (or something
>> similar), rather than simply omitting the information.
>> 
> Thanks for the suggestion.
> Yeah, just removing the Raid Level info is not the best option. I also
> considered to show it as "inactive Raid1" in such case.

If it would be a raid1 when activated, it is still a raid1 when
inactive: the data on disk doesn't suddenly become not a raid array
simply because the kernel isn't able to access it right now. This is
valuable information to expose to the sysadmin and should not be
concealed (and *certainly* not described as a raid level it actually
isn't).

I think it should say as much (if the system knows at this stage, which
if there is a device node, it presumably does).

Re: [RFC PATCH] Detail: don't display the raid level when it's inactive

[Zhong Lidong]

On 9/1/20 3:00 AM, Nix wrote:
> On 31 Aug 2020, Zhong Lidong told this:
> 
>> On 8/29/20 12:38 AM, Ian Pilcher wrote:
>>> On 8/26/20 10:16 AM, Lidong Zhong wrote:
>>>> ...
>>>> So the misleading "raid0" is shown in this testcase. I think maybe
>>>> the "Raid Level" item shouldn't be displayed any more for the inactive
>>>> array.
>>>
>>> As a system administrator, I'd much rather see "unknown" (or something
>>> similar), rather than simply omitting the information.
>>>
>> Thanks for the suggestion.
>> Yeah, just removing the Raid Level info is not the best option. I also
>> considered to show it as "inactive Raid1" in such case.
> 
> If it would be a raid1 when activated, it is still a raid1 when
> inactive: the data on disk doesn't suddenly become not a raid array
> simply because the kernel isn't able to access it right now. This is
> valuable information to expose to the sysadmin and should not be
> concealed (and *certainly* not described as a raid level it actually
> isn't).
> 
> I think it should say as much (if the system knows at this stage, which
> if there is a device node, it presumably does).
> 

Makes sense to me. I'll try to rewrite the patch.
Thanks for your share.

Regards,
Lidong