themaxxz Posted September 21, 2017 Share Posted September 21, 2017 (edited) Hi, Is unraid impacted by the 'skip_copy' problem described below? https://forum.synology.com/enu/viewtopic.php?t=135059 http://www.sbsfaq.com/?p=4277&doing_wp_cron=1505991093.5444660186767578125000 http://www.sbsfaq.com/?p=4321 Regards, Edited September 21, 2017 by themaxxz Quote Link to comment
SSD Posted September 21, 2017 Share Posted September 21, 2017 Extremely unlikely. unRaid uses parity and not RAID5 logic. Quote Link to comment
themaxxz Posted September 21, 2017 Author Share Posted September 21, 2017 27 minutes ago, bjp999 said: Extremely unlikely. unRaid uses parity and not RAID5 logic. You are probably right, but it would be nice to have confirmation from 'Lime Technology' directly. E.g. synology mentions that RAID 5, RAID 6, RAID F1, or SHR with more than 3 disks are impacted. Quote Link to comment
SSD Posted September 21, 2017 Share Posted September 21, 2017 UnRaid is different than RAID. UnRaid is not involved in the writing directly to the individual disks (although it must pass writes through from the md# device to the sdX device). It monitors those writes, computes parity, and writes parity. No data is striped across drives. It is a very difference paradigm from Raid. If parity were being corrupted, our parity checks would be showing that corruption. That's the only part that unRaid manages. So unless the issue is related to a problem with the handing off of writes, I doubt very much this affects unRaid. @limetech might be interested to know about this, and may be able to comment further.. Quote Link to comment
limetech Posted September 21, 2017 Share Posted September 21, 2017 First off, this does not affect unRAID becase the md/unraid driver diverged quite some time ago from 'stock' linux md driver. Interestingly what 'skip_copy' optimization does in stock md is something I've wanted to put into md/unraid for quite a while - I guess I need to re-think that idea 'skip_copy' is an optimization in stock linux md driver. I believe it was introduced here: https://www.spinics.net/lists/raid/msg46364.html The specific issue seen by QNAP and Synology (and all linux md based systems I suppose) is talked about here: https://www.spinics.net/lists/raid/msg59084.html This looks like a hairy bug to fix properly, though workaround is to disable skip_copy feature. (Again, not talking about unRAID here.) Edit: to be clear: I don't mean to imply anything about linux md integrity issue. The 'bug' was not introduced merely by adding the 'skip_copy' feature, I think it probably got introduced sometime after by other changes in the block layer in later kernels. Quote Link to comment
themaxxz Posted September 21, 2017 Author Share Posted September 21, 2017 Thanks for confirming there is no issue with unRAID. Quote Link to comment
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