2 ms·

>This feels a little disingenuous to me. This is a distinctly RAID-1 problem. This doesn't feel like a BTRFS problem. Everyone knows RAID-1 = 1 drive loss. Tha

by tw04 5y ago

>This feels a little disingenuous to me. This is a distinctly RAID-1 problem. This doesn't feel like a BTRFS problem. Everyone knows RAID-1 = 1 drive loss. That's simply not true. I can do a RAID-1 (mirror) with 3 drives on ZFS or mdadm and lose 2 drives. I can do it with 10 drives and lose 9. https://www.thegeekdiary.com/how-to-add-a-3rd-disk-to-create-a-3-way-mirror-raid1-md-device-centos-rhel-7/ https://www.thegeekdiary.com/how-to-add-a-3rd-disk-to-create... >There are many use cases for RAID-0, but the author is acting like this is some kind of problem with BTRFS. Sure, but for a novice the default advice needs to be: don't do that. And he's writing for folks with all sorts of levels of technical knowledge. Someone who knows nothing about RAID reading the article should be scared away unless they have a very, very good reason for doing RAID-0.

nybble41 5y ago
> I can do a RAID-1 (mirror) with 3 drives on ZFS or mdadm and lose 2 drives. You can do this with BTRFS also; it's called RAID1C3 (for three copies). RAID1C4 is also an option with larger arrays. The issue is that if you have, say, four drives and standard RAID-1 (two copies) it doesn't divide the drives into mirrored pairs where you could lose one drive from each pair without any ill effect (like RAID-10), but rather just ensures that each piece of data is stored on any two different drives. With 4-drive RAID-10 if you lose two drives you have a 50% chance of losing the whole array, since both failing drives could be from the same pair. With BTRFS RAID1 in a four-drive array you have a high probability of losing both copies of some of the data no matter which two drives fail. RAID-6 is strictly better than either, though, since you can lose any two drives and still access all your data.

2 ms·

>This feels a little disingenuous to me. This is a distinctly RAID-1 problem. This doesn't feel like a BTRFS problem. Everyone knows RAID-1 = 1 drive loss. Tha

by tw04 5y ago

nybble41 5y ago
> I can do a RAID-1 (mirror) with 3 drives on ZFS or mdadm and lose 2 drives. You can do this with BTRFS also; it's called RAID1C3 (for three copies). RAID1C4 is also an option with larger arrays. The issue is that if you have, say, four drives and standard RAID-1 (two copies) it doesn't divide the drives into mirrored pairs where you could lose one drive from each pair without any ill effect (like RAID-10), but rather just ensures that each piece of data is stored on any two different drives. With 4-drive RAID-10 if you lose two drives you have a 50% chance of losing the whole array, since both failing drives could be from the same pair. With BTRFS RAID1 in a four-drive array you have a high probability of losing both copies of some of the data no matter which two drives fail. RAID-6 is strictly better than either, though, since you can lose any two drives and still access all your data.