July 2, 201016 yr Why Not add a Second parity drive simply for redundancy / additional fault tolerance. It seems to me that the Achilles heel of the unraid system is the single parity drive. If two data drives fail you can always reconstruct the data from the parity. But if the parity & a data drive fail all data would be lost. A dual parity setup would effectively be like a raid 6 and provide much much greater fault redundancy Why not add the option for a second parity drive?
July 2, 201016 yr You don't understand how unRAID works to make that statement. It's not true in unRAID's case. With unRAID, if you lose the parity drive and a data drive, you only lose the contents on that single data drive. All the other data drives are perfectly fine.
July 2, 201016 yr As above, though I'd add an additional parity drive for improved resilience has been discussed before. Just not for the reasons you originally outlined!
July 2, 201016 yr As above, though I'd add an additional parity drive for improved resilience has been discussed before. Just not for the reasons you originally outlined! If an additional Parity drive could save you in the case where you lose 1 of 2 parities and a Data drive that would be cool. And/Or help you with the loss of two data drives. But I imagine a second parity would be more of a "hot swap" for the primary Parity drive. It would be nice for in increased level of fault tolerance for those that are especially wimpy.
July 2, 201016 yr A "hot" spare just for parity doesn't help much.... a hot spare should be able to replace ANY drive. RAID-6 has previously been announced to be in the works for a future version of unRAID .... the number and size of disks has now reached a point where real-world MTBF really justifies RAID-6, so I expect RAID-6 will be one of the next major features to be added to the core after 5.x is out.
July 2, 201016 yr Bubba, I agree. A "hot" spare just for parity doesn't help much.... a hot spare should be able to replace ANY drive. RAID-6 has previously been announced to be in the works for a future version of unRAID .... the number and size of disks has now reached a point where real-world MTBF really justifies RAID-6, so I expect RAID-6 will be one of the next major features to be added to the core after 5.x is out.
July 2, 201016 yr A "hot" spare just for parity doesn't help much.... a hot spare should be able to replace ANY drive. RAID-6 has previously been announced to be in the works for a future version of unRAID .... the number and size of disks has now reached a point where real-world MTBF really justifies RAID-6, so I expect RAID-6 will be one of the next major features to be added to the core after 5.x is out. I too would like a RAID6 dual parity approach, especially if it kept the current approach of not distributing parity across all the disks. I am not too worried about loosing some writing speed as a result of this, but I would expect that the current read speed (which is normally as fast as the drive the file being read is on) will be maintained under RAID6. So, yes, count me as a vote in favor of dual parity disks. Stephen
July 9, 201015 yr unRAID might be going to a dual parity configuration which would allow recovery from 2 simultaneous data drive failures. Tom discussed it in 1998 but it has not appeared yet. I'm thinking this may get implimented if (when) Tom increases the number of data drives again. http://lime-technology.com/forum/index.php?topic=2634.msg21695#msg21695 I don't believe unRAID will ever go to a RAID6 or other type of striped array because then it is no longer unRAID, but rather just another RAID solution. If two data drives fail you can always reconstruct the data from the parity. But if the parity & a data drive fail all data would be lost. OK, Neither of these scenarios are true. In the first case, you would lose the data on both of the failed data drives. In the second case you would lose the data on the single failed data drive. Peter
July 9, 201015 yr Tom discussed it in 1998 but it has not appeared yet. is that true? 1998 or 2008? If it's been 12 years already I wouldn't hold my breath.
July 11, 201015 yr I don't believe unRAID will ever go to a RAID6 or other type of striped array because then it is no longer unRAID, but rather just another RAID solution. The second parity drive idea mentioned by Tom, would *not* be a stripe, but rather another parity calculated using a Reed-Solomon code.
July 11, 201015 yr The second parity drive idea mentioned by Tom, would *not* be a stripe, but rather another parity calculated using a Reed-Solomon code. I understand how it is done with one parity disk, and I can even exlain it to someboy in simple words. But I can't imagine what the trick would be with a second parity disk. (I know what the desired result is)
July 11, 201015 yr Theoretically, you could use a large enough single parity drive with R/S to recover from loss of 2 data drives. But you would be exposed in the event of loss of 1 data and the parity drive.... so the regular parity drive can recover from that.
July 12, 201015 yr Almost seems like you would have to mirror your Parity drives, but maybe that could be something that was done after hours? Meaning have a primary Parity drive that did the day to day and have a second that would mirror late at night and or after a mirror would swap to secondary not to wear out the primary. We use that method at work when it comes to pumps. Do i have an exact schedule of when it should work or how? Welp not really, but I think if it mirrored on the fly it would really start to slow things down unless of course somebody else knew else wise.
July 12, 201015 yr Almost seems like you would have to mirror your Parity drives, but maybe that could be something that was done after hours? Meaning have a primary Parity drive that did the day to day and have a second that would mirror late at night and or after a mirror would swap to secondary not to wear out the primary. We use that method at work when it comes to pumps. Do i have an exact schedule of when it should work or how? Welp not really, but I think if it mirrored on the fly it would really start to slow things down unless of course somebody else knew else wise. It is NOT a mirror of a parity drive. That is useless. The parity drive is NO MORE IMPORTANT than any other drive if a data drive has failed. If anything, it is LESS important. (I'll explain later) The second "parity drive" you are referring to is not a parity drive at all. It is an entirely different calculation, similar to Raid-6, It is a "Reed-Salomon code drive" done in a different fashion across all the data drives including parity. It will provide additional protection from a double drive failure, but at a cost. That cost is efficiency. It will slow the write speed of the array, perhaps drastically. as far as the current unRAID parity drive being LESS important than any other drive... let me explain... Let's assume you have 2 data disks and a parity disk. (you are using the free version of unRAID) Let's assume one of your data disks fails. Now parity and the remaining data disk are able to simulate the failed drive. This is good. Now, which of the two remaining drives is more important? Let's see... Scenario 1. Let's assume you have really bad luck and the parity drive were to also fail. You would lose the ability to simulate any data drive. By having one data drive and the parity drive fail at the same time, you've lost 50% of your data. The second data drive is still readable and perfectly fine. Scenario 2. Let's say you have really horrible luck, and instead of the parity drive failing,the second data drive were to fail instead. Again, you would lose the ability to simulate any failed data drive. By having both data drives fail at the same time, you've lost 100% of your data, even though you have a perfectly good parity drive. Looks to me that a loss of a parity drive is less critical than a loss of any data drive A loss of two drives, where one is the parity drive results in a loss of 1/Nth of your data. (where N = number of data drives in the array) A loss of two drives, where neither is the parity drive results in a loss of 2/Nth of your data. (where N = number of data drives in the array) Joe L.
July 18, 201015 yr Hi, Just read this about a second parity and its exactly what im looking for! Is this going to be release for v5 pro? And what happens if I buy v4,5 pro would I be upgrade for free?
July 18, 201015 yr Hi, Just read this about a second parity and its exactly what im looking for! Is this going to be release for v5 pro? I believe 5.0 is a complete interface change. I would think any changes to the raid subsystem would come at a later time. And what happens if I buy v4,5 pro would I be upgrade for free? Yes, Currently you can upgrade for free.
July 21, 201015 yr Just FYI, heh: http://lime-technology.com/forum/index.php?topic=5342.0 That said, I want this to happen, so more threads, more threads!
August 6, 201015 yr What if instead of mirroring the parity drive, it could be assigned to different sets of drives... Parity1 could protect discs 1-10, Parity2 could protect drives 11-20. That way you could have 2 drives fail at once with a 50 percent change of surviving without losing a single bit of data
August 6, 201015 yr Not to pick nits here, but isn't that the same configuration as having 2 unRAID arrays?
August 6, 201015 yr Not to pick nits here, but isn't that the same configuration as having 2 unRAID arrays? Yes. That's identical to having 2 unRAID arrays.
August 6, 201015 yr Except if you had two unRAIDs, then you'd have to deal with two html interfaces, two unmenus, two sets of user shares (Was that movie on unRaid1 or unRaid2??) Ideally you could have one unRaid configuration, with as many configurable parity protections as you wish...
August 6, 201015 yr JustinAiken, not true. You have one management console but multiple arrays on the same server. This is the feature you're requesting which has been requested before. Do not confuse "unRAID array" with "unRAID Servers". In normal Linux, it's possible to use a single server to have multiple software-raid arrays. It's management console is "mdadm". [ http://en.wikipedia.org/wiki/Mdadm ] It's typical usage for multiple arrays is something like: mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sda1 /dev/sdb1 mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sda2 /dev/sdb2 /dev/sdc2 Your request of having parity drive 1 for data drives 1-10 and parity drive 2 for data drives 11-20 is exactly supporting multiple unRAID Arrays within a single unRAID Server.
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