-----Original message----- From: Brendan Hide <bren...@swiftspirit.co.za> Sent: Fri 01-23-2015 08:18 pm Subject: Re: Recovery Operation With Multiple Devices To: Brett King <brett.k...@commandict.com.au>; linux-btrfs@vger.kernel.org; > On 2015/01/23 09:53, Brett King wrote: > > Hi All, > > Just wondering how 'btrfs recovery' operates > I'm assuming you're referring to a different set of commands or general > scrub/recovery processes. AFAIK there is no "btrfs recovery" command. >
Oh yes, my apologies - I did mean 'btrfs restore' as a means of recovery. > > , when the source device given is one of many in an MD array - I can't find > anything documentation beyond a single device use case. > btrfs doesn't know what an md array or member is, therefore your results > aren't going to be well-defined. Depending on the type of md array the > member was in, your data may be mostly readable (RAID1) or > completely/mostly non-interpretable (RAID5/6/10/0) until md fixes the array. > Apologies again, by 'MD' I mean btrfs multiple devices not the MD for block-level RAID via mdadm. > > Does it automatically include all devices in the relevant MD array as > > occurs > when mounting, or does it only restore the data which happened to be written > to > the specific, single device given ? > As above, btrfs is not md-aware. It will attempt to work with what it is > given. It might not understand anything it sees as it will not have a > good description of what it is looking at. Imagine being given > instructions on how to get somewhere only to find that the first 20 > instructions and every second instruction thereafter was skipped and > there's a 50% chance the destination doesn't exist. > > > From an inverse perspective, how can I restore all data including > > snapshots, > which are spread across a damaged MD FS to a new (MD) FS ? > Your best bet is to restore the md array. More details are needed for > anyone to assist - for example what RAID-type was the array set up with, > how many disks were in the array, and how it failed. Also, technically > this is the wrong place to ask for advice about restoring md arrays. ;) > The FS is btrfs RAID1 and gets forced readonly from what appears to be related to the 3.17 snapshot bug. > > Can send / receive do this perhaps ? > Send/receive is for sending good data to a destination that can accept > it. This, as above, depends on the data being readable/available. Very > likely the data will be unreadable from a single disk unless the md > array was RAID1. > I can read the data fine and tried the 'btrfs restore -sxv', which appeared to do what I wanted but I don't yet have enough space on the restore target to confirm that it gets more data than the single source disk I specify on the command. > > Thanks in advance ! > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > the body of a message to majord...@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- > __________ > Brendan Hide > http://swiftspirit.co.za/ > http://www.webafrica.co.za/?AFF1E97 > > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
