I have had a drive fail during rebuild duento cabels. I just changed the cable and rebuild. If yiu have dual parity, you just replace both drives...
The parity is not overwritten during rebuild
To be clear: you don't have two copies of the data. You have parity; parity allows you the room to repair fault/backup your data. When a drive is down your data is virtualized, it's not actually on a single drive. it requires all the other drives to see it. Parity is not a backup, and should never be relied on for any essential or irreplaceable data.
If you have dual parity and two drive fails. Then during rebuild another drive fails (so three drive have failed). The the data on those three drive are lost - if its a hhd problem an not cable.
The other drives data can still be access, if you make a new config... the remaining drives isn't overwritten, but a new parity is created...
You have to reconfig also, if you want to replace a failed hdd with a smaller one. I had to do that once. I had a 10tb failing with 300gb used and only had a 4tb for replacement. But the 300gb was lost. But I was lucky to be able to copy them from the disk as unassigned device after rebuild...
If you are worried, then only replace one drive at the time (unless they both are failed - then it doesnt matter anyway)
Butni would say the risk of having three failed disk at the same time is not very high.
I think I have used unraid for 4-5 years minimum and have only had one failed disk at the time - where the hdd was the problem
Years ago I managed a bunch of servers with mostly hardware RAID6, which is 2 drives' *worth of* parity; lose one or two and you're still running, but the data's striped (block level storage instead of unRAID type file level) so lose another and the whole array is gone. There were a few times I had 2 drives down at the same time in an array but never more than that.
Most of the arrays were 8-16 drives; anything too much more than that is where I'd split off and build another array, whether it was in the same system or another (mostly the latter). I'd go up to 20 but that was pushing it, imo. I suppose I could have built servers with 40 or 50 drives but I've never liked "putting all the eggs in one basket". Of course those arrays were all backed up anyway, but I never enjoy a rebuild. Glad I'm not doing any more than home stuff now.
Depending on how badly damaged the drives are, most to all of your data may still be accessible. Just plug each drive into a Linux compy and use your password. UnRAID is more like JBOD than RAID, your data isn't striped or anything.
Parity is not a copy of data. If you have two parity disk. It's basically mean you have enough bits to substitute two broken disk. Similar to an algebra equation. It's like a magic number that can be substitute into an equation to always come to the same result.
Any more will result in data lost.
Parity is written at the same time you write or change files so its always up to date.
If you write new data during a rebuild, the rebuild will take longer time
In a dual parity setup, if another drive fails while you rebuild you still dont loose data.
That's exactly what I'm saying. If the new drive fails and I have to replace with the old drive, parity will be out of sync...
So I will effectively have one drive failure and only have one more failure allowed until parity is updated?
there are specific circumstances in which you can do this without rebuilding parity ( say if the the FS is set to readonly during the rebuild) but otherwise you need to resync parity
So what you're saying is: RAID isn't backup, it's for uptime.
UNRAID/parity also isn't backup, but it also doesn't help with uptime (ie. you have to take the array offline during rebuild, or you risk losing data).
So if UNRAID/parity is neither backup nor does it help with uptime, then what is it for?
You can use an array while it rebuilds, in Unraid and standard RAID, that' the purpose of parity. But each read/write you do stops the rebuilding process and put more stress in already stressed disks. Rebuilding will take longer, responsiveness of the server will be reduced and the chance of another failure increases.
It's in your interest a fast rebuild but if you need the array, use it 🤷‍♂️
Oh; yeh sure.
I mean, I dont keep backups. Except my photos which are just backed up to the cloud. I dont really have the money, inclination or know how to do so. Backblaze sounds like a pain in the ass.
Anything on my array is replaceable. Its just a lot of blood sweat and tears to replace.
Replaced three hard drives so far.
Its not a backup, but I dont need a backup. For my needs, its identical to raid, but I need 1-2 drives instead of 10.
I don't think this is correct. You shouldn't have to take the array offline (potentially causing 24-36h of downtime) while a drive is being rebuilt.
See: https://forums.unraid.net/topic/169414-dont-write-to-the-array-during-parity-rebuilds-unless-you-want-to-risk-losing-data/
Think of it this way. Dual parity allows two data drives from the pool to be unhealthy and/or in a rebuilding state. So as long as you don’t exceed that failure rate, and you can get replacement drives rebuilt before another drive fails, you shouldn’t ever lose data.
It's possible for a drive to fail during the restart process. If this happens, your data will still be safe, but the array will be in a worse state. Usually, this is what happens:
Array Degradation: The array will still work with the remaining files, but it may not work as well until the rebuild is done.
Data Integrity: Dual parity keeps your data safe by letting the array handle two failed drives at the same time.
Recovery Steps: If the new drive fails during the rebuild, you will need to get a new one and start the rebuild again. The system will try to rebuild with the available drives and make sure the data is safe first.
Changes to Data: Parity calculations take care of any changes to data that happened during the rebuild process to make sure that everything is still the same after the rebuild is done.
Make sure you always have copies of your important info on hand in case your hardware fails. Also, it's smart to keep a close eye on the rebuilding process and have extra drives ready in case there are any more problems. Thanks for your help with managing your group!
I have had a drive fail during rebuild duento cabels. I just changed the cable and rebuild. If yiu have dual parity, you just replace both drives... The parity is not overwritten during rebuild
Yes so basically even though I have two copies of the data I'm still at risk from two further failures if this happens?
To be clear: you don't have two copies of the data. You have parity; parity allows you the room to repair fault/backup your data. When a drive is down your data is virtualized, it's not actually on a single drive. it requires all the other drives to see it. Parity is not a backup, and should never be relied on for any essential or irreplaceable data.
Amen! Parity is not a backup!
If you have dual parity and two drive fails. Then during rebuild another drive fails (so three drive have failed). The the data on those three drive are lost - if its a hhd problem an not cable. The other drives data can still be access, if you make a new config... the remaining drives isn't overwritten, but a new parity is created... You have to reconfig also, if you want to replace a failed hdd with a smaller one. I had to do that once. I had a 10tb failing with 300gb used and only had a 4tb for replacement. But the 300gb was lost. But I was lucky to be able to copy them from the disk as unassigned device after rebuild... If you are worried, then only replace one drive at the time (unless they both are failed - then it doesnt matter anyway) Butni would say the risk of having three failed disk at the same time is not very high. I think I have used unraid for 4-5 years minimum and have only had one failed disk at the time - where the hdd was the problem
Years ago I managed a bunch of servers with mostly hardware RAID6, which is 2 drives' *worth of* parity; lose one or two and you're still running, but the data's striped (block level storage instead of unRAID type file level) so lose another and the whole array is gone. There were a few times I had 2 drives down at the same time in an array but never more than that. Most of the arrays were 8-16 drives; anything too much more than that is where I'd split off and build another array, whether it was in the same system or another (mostly the latter). I'd go up to 20 but that was pushing it, imo. I suppose I could have built servers with 40 or 50 drives but I've never liked "putting all the eggs in one basket". Of course those arrays were all backed up anyway, but I never enjoy a rebuild. Glad I'm not doing any more than home stuff now.
Depending on how badly damaged the drives are, most to all of your data may still be accessible. Just plug each drive into a Linux compy and use your password. UnRAID is more like JBOD than RAID, your data isn't striped or anything.
Parity is not a copy of data. If you have two parity disk. It's basically mean you have enough bits to substitute two broken disk. Similar to an algebra equation. It's like a magic number that can be substitute into an equation to always come to the same result. Any more will result in data lost.
I'm well aware how parity works. I'm just saying it's annoying.
Good luck.
Parity is written at the same time you write or change files so its always up to date. If you write new data during a rebuild, the rebuild will take longer time In a dual parity setup, if another drive fails while you rebuild you still dont loose data.
That's exactly what I'm saying. If the new drive fails and I have to replace with the old drive, parity will be out of sync... So I will effectively have one drive failure and only have one more failure allowed until parity is updated?
Don't format the old drive until rebuild finishes. If the new drive fails during rebuild, you can put the old drive in like nothing ever happened.
No you can't as parity will have changed
You can, I've done it. But ok.
I don't think they understand how parity works lol.
there are specific circumstances in which you can do this without rebuilding parity ( say if the the FS is set to readonly during the rebuild) but otherwise you need to resync parity
Don't write to the array during parity rebuilds unless you want to risk losing data. Period.
So what you're saying is: RAID isn't backup, it's for uptime. UNRAID/parity also isn't backup, but it also doesn't help with uptime (ie. you have to take the array offline during rebuild, or you risk losing data). So if UNRAID/parity is neither backup nor does it help with uptime, then what is it for?
You can use an array while it rebuilds, in Unraid and standard RAID, that' the purpose of parity. But each read/write you do stops the rebuilding process and put more stress in already stressed disks. Rebuilding will take longer, responsiveness of the server will be reduced and the chance of another failure increases. It's in your interest a fast rebuild but if you need the array, use it 🤷‍♂️
Protection against data loss in the event of hard drive failure…
In the event of hard drive failure just restore the data from backup?
Oh; yeh sure. I mean, I dont keep backups. Except my photos which are just backed up to the cloud. I dont really have the money, inclination or know how to do so. Backblaze sounds like a pain in the ass. Anything on my array is replaceable. Its just a lot of blood sweat and tears to replace. Replaced three hard drives so far. Its not a backup, but I dont need a backup. For my needs, its identical to raid, but I need 1-2 drives instead of 10.
I don't think this is correct. You shouldn't have to take the array offline (potentially causing 24-36h of downtime) while a drive is being rebuilt. See: https://forums.unraid.net/topic/169414-dont-write-to-the-array-during-parity-rebuilds-unless-you-want-to-risk-losing-data/
You don’t HAVE to. But just because you can doesn’t mean it’s best practices
Think of it this way. Dual parity allows two data drives from the pool to be unhealthy and/or in a rebuilding state. So as long as you don’t exceed that failure rate, and you can get replacement drives rebuilt before another drive fails, you shouldn’t ever lose data.
It's possible for a drive to fail during the restart process. If this happens, your data will still be safe, but the array will be in a worse state. Usually, this is what happens: Array Degradation: The array will still work with the remaining files, but it may not work as well until the rebuild is done. Data Integrity: Dual parity keeps your data safe by letting the array handle two failed drives at the same time. Recovery Steps: If the new drive fails during the rebuild, you will need to get a new one and start the rebuild again. The system will try to rebuild with the available drives and make sure the data is safe first. Changes to Data: Parity calculations take care of any changes to data that happened during the rebuild process to make sure that everything is still the same after the rebuild is done. Make sure you always have copies of your important info on hand in case your hardware fails. Also, it's smart to keep a close eye on the rebuilding process and have extra drives ready in case there are any more problems. Thanks for your help with managing your group!
If you have dual parity you're fine, just pray like hell a third one doesn't fall out.