On Fri, 26 Jul 2013 23:06:01 +0200 Martin Wilck <mwilck@xxxxxxxx> wrote: > Hi Neil, > > here is another question. 2 years ago you committed c7079c84 "ddf: > remove failed devices that are no longer in use", with the reasoning "it > isn't clear what (a phys disk record for every physically attached > device) means in the case of soft raid in a general purpose Linux computer". > > I am not sure if this was correct. A common use case for DDF is an > actual BIOS fake RAID, possibly dual-boot with a vendor soft-RAID driver > under Windows. Such other driver might be highly confused by mdadm > auto-removing devices. Not even "missing" devices need to be removed > from the meta data in DDF; they can be simply marked "missing". > > May I ask you to reconsider this, and possibly revert c7079c84? > Martin You may certainly ask .... I presumably had a motivation for that change. Unfortunately I didn't record the motivation, only the excuse. It probably comes down to a question of when *do* you remove phys disk records? I think that if I revert that patch we could get a situation where we keep adding new phys disk records and fill up some table. We should probably be recording some sort of WWN or path identifier in the metadata and then have md check in /dev/disk/by-XXX to decide if the device has really disappeared or is just failed. Maybe the 'path' field in phys_disk_entry could/should be used here. However we the BIOS might interpret that in a specific way that mdadm would need to agree with.... If we can come up with a reasonably reliable way to remove phys disk records at an appropriate time, I'm happy to revert this patch. Until then I'm not sure it is a good idea..... But I'm open to being convinced. Thanks, NeilBrown
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