misc/76209: geom metadata/label ambiguity with last slices - mirror, label etc

[Cyril Vechera]

>Number:         76209
>Category:       misc
>Synopsis:       geom metadata/label ambiguity with last slices - mirror, label etc
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Jan 13 16:40:24 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Cyril Vechera
>Release:        5.3
>Organization:
Net Ltd.
>Environment:
FreeBSD 2.tester.local 5.3-STABLE FreeBSD 5.3-STABLE #0: Thu Jan 13 15:35:36 UTC 2005     root at tester.local:/usr/obj/usr/src/sys/GENERIC  i386
>Description:
When geom based subsystems writes metadata on a hard disk there is possible ambiguity with nested slices. Becouse of geom label is stored in the last sector of provider's slice, it can beloing to either parent or child slice, for example to ad0 and ad0s4 and ad0s4h. This ambiguity can result a problems with geom system configuration, rebuilding and data loss.
>How-To-Repeat:
2# disklabel ad1s2
# /dev/ad1s2:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 480008592        0    unused        0     0         # "raw" part, don't edit
  e: 134217728        0    unused        0     0
  f: 345790864 134217728    unused        0     0
2# gmirror label block1 ad1s2e
2# gmirror label block2 ad1s2f
2# gmirror list
Geom name: block2
State: COMPLETE
Components: 1
Balance: split
Slice: 4096
Flags: NONE
SyncID: 1
ID: 4101347184
Providers:
1. Name: mirror/block2
   Mediasize: 177044921856 (165G)
   Sectorsize: 512
   Mode: r0w0e4
Consumers:
1. Name: ad1
   Mediasize: 250059350016 (233G)
   Sectorsize: 512
   Mode: r0w0e6
   State: ACTIVE
   Priority: 0
   Flags: NONE
   SyncID: 1
   ID: 637386526

Geom name: block2.sync

Geom name: block1
State: COMPLETE
Components: 1
Balance: split
Slice: 4096
Flags: NONE
SyncID: 1
ID: 1722957731
Providers:
1. Name: mirror/block1
   Mediasize: 68719476224 (64G)
   Sectorsize: 512
   Mode: r0w0e0
Consumers:
1. Name: mirror/block2s2e
   Mediasize: 68719476736 (64G)
   Sectorsize: 512
   Mode: r0w0e0
   State: ACTIVE
   Priority: 0
   Flags: NONE
   SyncID: 1
   ID: 4201844369

Geom name: block1.sync

We have mirror/block2 thinking that his consumer is ad1 instead of ad1s2f

>Fix:
Maybe we have to store a name of provider as a hint in a label written on a disk.

Quick workaround to avoid the problem is to shrink last nested slice on 1 sector to make different the last sector of a "geomed" slice and last sector of parent slice.
>Release-Note:
>Audit-Trail:
>Unformatted: