6 ms·
RAID 1 still has benefit when coupled with proper backup. Can still replace a drive and keep working faster than doing a restore from backup for large drives.
by rietta 6y ago
RAID 1 still has benefit when coupled with proper backup. Can still replace a drive and keep working faster than doing a restore from backup for large drives.
- rzzzt 6y agoWith current failure rates, isn't one running the risk of hitting a URE while creating the first backup?
- ghaff 6y agoAt the right cost points have a three-way mirror?
- rietta 6y agoA RAID does not increase the risk of a drive failure. It via redundancy reduces the risk, but not to zero. Probability of Single Drive Failure > Probability of Double Drive Failure. RAID is not a backup, so still need that backup. 1. Without RAID, drive fails and you're stuck waiting for restore from backup. 2. With RAID, risk double drive fails < risk of #1 and are stuck waiting for restore from backup. 3. With RAID, risk of single drive fails > 0 and < #2 and continue working while waiting on drive clone while still having the backup in #1 and #2 to fall back on.
- rietta 6y agoCompared to what? The general argument for "no raid" is to have a single drive without redundancy other than backup. That's riskier than a mirror.
- rzzzt 6y ago120 TB drives compared to 4-8-12-ish TB drives. I'm wondering if there is a chance of ever completing operations targeting the entire disk (be it an initial RAID build, resilver, restore or full backup) without hitting a speed bump.
- Dylan16807 6y agoIs that a statistic that matters? If I have a bunch of 8TB drives, I don't care what my odds are of doing a single-drive operation without a speed bump. I'm going to back them all up at the same time, and I only care about speed bumps over the entire operation and how well they're handled.
- effie 6y agoURE is a read error, not a drive failure. So yes bigger disk increases chance of silent and loud UREs, but with URE rate 1e-15, for RAID1 disks up to 40TB are usable (you can redo the rebuild if it fails, or simply ignore the loss of data in many cases). If we ever get to 100TB drives, their URE rate will probably go down as well. This and low demand will probably make them quite expensive.
- throwaway81523 6y agoSince the drives are full of ECC already, do UREs result from multiple simultaneous errors? Can that be fixed with even more ECC? I.e. if the errors are reasonably independent, you could change 1e-14 URE rate to 1e-18 or whatever you wanted, by just adding more ECC, in principle of size logarithmic in the size of the disk (though you might want to cache it in ram in such a case). That is how tape drives work, I think. The put ECC codes into blocks on the tape, then erasure codes over clusters of blocks, then more erasure codes over clusters of clusters, etc. RAID amounts to doing that over entire disks, after all.
- effie 6y agoI think UREs due to problems with medium (magnetic layer) can be eliminated to arbitrarily small rate with more and better ECC. However I think (probably small) part of the total URE rate are randomly occurring errors due to intermittent mechanical and electronic failures, mostly due to random environment influences. Eliminating those would require technology improvement beyond more ECC on the platter. Probably more ECC and higher quality of all components along the whole datapath. Maybe the above is wrong because UREs are just the unrecoverable medium errors. I can't find the official definition of URE rate.