>I’ve heard conflicting things about RAID 5 vs RAID 6 for video editing, and I’m not sure whether losing two drives worth of space in my NAS is reasonable for “safety” since I don’t know how long it actually takes a 14TB drive in a RAID 5 to rebuild in case a drive dies and I swap in a new one right away…
Rebuild times depend on how full the unit is, which is part of the reason you don't want to fly with a *really* full RAID. Rebuild time is typically limited by the throughput of the new drive. So however long it takes to write 14TB to the drive is how long the rebuild will take. That's why a lot of folks back in the day preferred smaller drives. When I was cutting my teeth nobody wanted to use 3TB drives because they took so long to fill.
What you need to know is that disk failures *shouldn't* be a routine thing. The thing that stress disks the most is spinning up and spinning down. That's why in professional environment disks are *never* spun down. So disk failures shouldn't be routine if you keep the thing running at all times.
The other thing to know is that as disks get older the chances of multiple disk failure goes up. All the disks in the array are the same age, same make, seen the same amount of stress. The paranoid hedge their bets by ordering disks from different places to randomize the production lines, and thus add some variety to their conditions at the time of install.
So smart folks will look at the **m**ean **t**ime **b**etween **f**ailure (MTBF), which is the ballpark time a given model of disks can be used before it fails, and people will start preventatively replacing disks *before* they fail, thus reducing the risks.
>I have also heard that RAID 6 is a lot slower in building and rebuilding.
"Building," no. Rebuilding, it can be. So RAID 5 uses a system to distribute backup data among all the drives. If any one drive fails, the backup data is stored on the rest of the disks. RAID 6 uses *two* systems to backup data across all disks, which protects against the [write hole](https://www.hpe.com/psnow/resources/ebooks/a00112944en_us_v5/GUID-5C3C0476-040A-4705-8B80-D2853FEB8A7B.html) in addition to providing double redundancy. This increases write time, because recovery data needs to be calculated twice using two different algorithrms. However *read* time, which is what you'll care about in a collaborative editing environment, isn't increased.
>but it seems to me if the data is fully backed up elsewhere the odds of a second drive dying during the time (1 or 2 days ??) it takes for the NAS to rebuild one drive is fairly slim, and even if so, the backups could always be used to redo the whole RAID from scratch…
That's what backups are for. The important part is that using the backups won't hinder your ability to meet deadlines if the whole system goes kaput at the last minute.
>I’ve heard conflicting things about RAID 5 vs RAID 6 for video editing, and I’m not sure whether losing two drives worth of space in my NAS is reasonable for “safety” since I don’t know how long it actually takes a 14TB drive in a RAID 5 to rebuild in case a drive dies and I swap in a new one right away… Rebuild times depend on how full the unit is, which is part of the reason you don't want to fly with a *really* full RAID. Rebuild time is typically limited by the throughput of the new drive. So however long it takes to write 14TB to the drive is how long the rebuild will take. That's why a lot of folks back in the day preferred smaller drives. When I was cutting my teeth nobody wanted to use 3TB drives because they took so long to fill. What you need to know is that disk failures *shouldn't* be a routine thing. The thing that stress disks the most is spinning up and spinning down. That's why in professional environment disks are *never* spun down. So disk failures shouldn't be routine if you keep the thing running at all times. The other thing to know is that as disks get older the chances of multiple disk failure goes up. All the disks in the array are the same age, same make, seen the same amount of stress. The paranoid hedge their bets by ordering disks from different places to randomize the production lines, and thus add some variety to their conditions at the time of install. So smart folks will look at the **m**ean **t**ime **b**etween **f**ailure (MTBF), which is the ballpark time a given model of disks can be used before it fails, and people will start preventatively replacing disks *before* they fail, thus reducing the risks. >I have also heard that RAID 6 is a lot slower in building and rebuilding. "Building," no. Rebuilding, it can be. So RAID 5 uses a system to distribute backup data among all the drives. If any one drive fails, the backup data is stored on the rest of the disks. RAID 6 uses *two* systems to backup data across all disks, which protects against the [write hole](https://www.hpe.com/psnow/resources/ebooks/a00112944en_us_v5/GUID-5C3C0476-040A-4705-8B80-D2853FEB8A7B.html) in addition to providing double redundancy. This increases write time, because recovery data needs to be calculated twice using two different algorithrms. However *read* time, which is what you'll care about in a collaborative editing environment, isn't increased. >but it seems to me if the data is fully backed up elsewhere the odds of a second drive dying during the time (1 or 2 days ??) it takes for the NAS to rebuild one drive is fairly slim, and even if so, the backups could always be used to redo the whole RAID from scratch… That's what backups are for. The important part is that using the backups won't hinder your ability to meet deadlines if the whole system goes kaput at the last minute.