4 ms·

I don't get why you need to do so. RAID is not a substitute of backups, and shouldn't used that way. Meaning that of course you have a backup of the data that y

I don't get why you need to do so. RAID is not a substitute of backups, and shouldn't used that way. Meaning that of course you have a backup of the data that you can recover from. RAID is used for two things: 1. improving the performance of slow disks (at least the read performance) 2. having 1/2 disk fail with your system remaining completely usable, till you replace the faulty disk as soon as possible. The second point is fundamental to me: there shouldn't be any disruption of service whatsoever, meaning that only the sysadmin should notice the fault (beside maybe a reduced performance of the system since you have 1 less drive). Database transaction that were in progress when the disk did break shouldn't fail, writes/reads on the FS shouldn't fail, the only thing that should happen is an alarm triggered in the monitoring system to inform that a disk needs to be changed as soon as possible. Having a RAID with manual recovery... it means that you could end up a Saturday evening in front of a computer to bring a system back online, and still some data corruption may have happened.

dekhn 4y ago
Regardless of what you think, many people keep a separate boot and data disk and don't use RAID on the boot disk. I never said anything about it being used for backups nor did I said anything about service outages. I think my point- about what other people do since I don't use RAID- is more about the choices different people make in terms of trusting their boot volume's recoverability in times of crisis.
linuxandrew 4y ago
3. Prevent bit-rot w/ software RAID. Running ZFS, btrfs et al. on a single disk can detect bit-rot but not repair it.
- _kdave 4y ago
  By default the metadata profile is 'DUP' (i.e. 2 copies on one device), the same can be done for data but this reduces the usable capacity. On normal HDD or SSD this should not be needed but having both data and metadata DUP/DUP has been useful on raspberry pi with the micro SD card storage. It's not perfect but increases the chances to get the data back if the card is partially damaged due to power spikes.
  - ac29 4y ago
    I have wondered about this myself - does keeping 2 copies of the same data on a single flash-based drive actually increase reliability? Or is the flash controller going to end up combining the two writes into the same block?

dekhn 4y ago

Regardless of what you think, many people keep a separate boot and data disk and don't use RAID on the boot disk. I never said anything about it being used for backups nor did I said anything about service outages. I think my point- about what other people do since I don't use RAID- is more about the choices different people make in terms of trusting their boot volume's recoverability in times of crisis.

linuxandrew 4y ago

3. Prevent bit-rot w/ software RAID. Running ZFS, btrfs et al. on a single disk can detect bit-rot but not repair it.

_kdave 4y ago
By default the metadata profile is 'DUP' (i.e. 2 copies on one device), the same can be done for data but this reduces the usable capacity. On normal HDD or SSD this should not be needed but having both data and metadata DUP/DUP has been useful on raspberry pi with the micro SD card storage. It's not perfect but increases the chances to get the data back if the card is partially damaged due to power spikes.
- ac29 4y ago
  I have wondered about this myself - does keeping 2 copies of the same data on a single flash-based drive actually increase reliability? Or is the flash controller going to end up combining the two writes into the same block?