March 29, 201610 yr Hey there! My unRAID Server is doing pretty great atm, however i was thinking about adding a parity device, now that all my files are transfered and write speed isnt that much of a problem (i have a 240gb SSD Cache for all the smaller transfers that will follow) However i still have a view questions about how it actualy works: 1. Im using Btrfs as Filesystem and since it can detect corrupted sectors it needs some sort of redundancy to repair them (like btrfs raid1), but is a parity enough? Will it automaticly repair those broken sectors? (by broken i mean like corrupted by bit rod or something like that not physicly damaged) 2. Will it require all my drives to spin up when i add new data to create the cross sum? 3. There will be lots of traffic on the parity, so would you consider using enterprise Hardware here? 4. where will the cross sum calculation take place? Or in other words: Faster CPU = Faster rightspeed? Drop whatever info you have on this topic and thank you very much for sharing your knowledge! (Sry if i messed something up here, i just fell out of my bed... )
March 29, 201610 yr Presently, the parity can't be used to do anything with corruption as reported by BTRFS. I'm doubtful anything will change in the future but I could be wrong. Unless you are expecting to be writing to multiple drives at the same time I wouldn't use any special hardware for the parity drive. I would just use a drive at least as good as your data drives. All drives need to be spinning to create the initial parity data, but not to write data to a single disk once the parity is in place.
March 29, 201610 yr Author Thanks for your answer! Is it possible to recreate single Files from the parity (like a Jpeg that has been reported corrupted)? Otherwise i dont realy see the point in having a parity device... This basicly only leaves my last question: Will a faster CPU provide higher rightspeed?
March 29, 201610 yr Thanks for your answer! Is it possible to recreate single Files from the parity (like a Jpeg that has been reported corrupted)? Otherwise i dont realy see the point in having a parity device... This basicly only leaves my last question: Will a faster CPU provide higher rightspeed? No, the parity drive cannot be used to recreate a single file. It is used to recreate entire failed disks (and sooner or later, one of your disks WILL fail, and at that point you will be kicking yourself if you don't have a parity disks)
March 29, 201610 yr Author I do have full Backups on seperate drives, so i could just copy them onto the new disk... (however at that point i only have one copy of the files in question, which adds some extra risk. I did some reading in the wiki and found this: There are only two situations that the parity data is used by unRAID to reconstruct data: when a disk is being reconstructed; and when a bad sector is detected. To me this sounds like it does actualy repair bad sectors by itself... btw: Thanks for your reply
March 29, 201610 yr I do have full Backups on seperate drives, so i could just copy them onto the new disk... (however at that point i only have one copy of the files in question, which adds some extra risk. I did some reading in the wiki and found this: There are only two situations that the parity data is used by unRAID to reconstruct data: when a disk is being reconstructed; and when a bad sector is detected. To me this sounds like it does actualy repair bad sectors by itself... btw: Thanks for your reply a bad sector (read error on a disk) and what you were talking about a corrupted file are not the same thing (although a read error will cause a corrupted file - in which case the parity disk will fix that automatically)
March 29, 201610 yr Author So for the parity to kick in the sector must be reported as bad like broken on hardware level? Not just corrupted like btrfs can tell?
March 29, 201610 yr Author Great, so the only question remaining is how to boost write (i actually mistyped that like a hundred times) performance. To me it seems like the only way is to get faster spinning drives since the actual read/write count seems to be the limiting factor. Getting a faster spinning would only boost writes to multible disks but not to a single one i assume.
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