3 ms·

I don't think this works. With more drives, you expect more drives to die in the same time period, so total expected loss stays exactly constant.

by gcp 10y ago

mdorazio 10y ago
Yes, but they don't all die at the same time, so you can utilize a RAID or similar array to mitigate the failures at a small cost in total storage space. Ex. my 5-drive RAID array runs 5x 3TB drives and provides about 12TB of usable space. If any single drive fails, it's a quick swap with a cheap replacement. If I instead had a single 12TB drive fail, I'd be screwed. Even if I didn't have a RAID array, any single drive failure would be a maximum of 3TB lost, vs. losing everything with a single drive. Basically it's much easier to minimize your data loss risk profile if you spread your data across multiple drives instead of relying on a single drive. Of course, if you need 100TB+ of storage, you might as well put these new 16TB drives in an array and save on the controller costs.
- zzalpha 10y ago
  And then if there's an unrecoverable read error on one of those other massive drives during the rebuild, you're in deep trouble.. and the bigger the drive the more likely this is to happen (reaching near-certainty once the drive is large enough): http://www.zdnet.com/article/why-raid-5-stops-working-in-2009/ http://www.zdnet.com/article/why-raid-5-stops-working-in-200...
  - snuxoll 10y ago
    Which is why the 3 and 4TB drives I have in my FreeNAS box at home are configured as mirrored pairs, the time it takes to resliver a drive in this configuration is already fairly long - RAID-Z or the hardware equivalent of RAID-5 would take upwards of days to complete and that's a disaster waiting to happen.
- cmurf 10y ago
  At this size, the rebuild time is a day, or even 2-3 days if it's actively being used during the rebuild. It still makes sense to do at least a 2x raid1, which rebuilds faster than a cluster over wired ethernet. But if you have this much online storage, you probably have a high availability need also, which implies cluster in case a storage brick loses a power supply or logic board. It's not just a drive that can fail.

I don't think this works. With more drives, you expect more drives to die in the same time period, so total expected loss stays exactly constant.

by gcp 10y ago

I don't think this works. With more drives, you expect more drives to die in the same time period, so total expected loss stays exactly constant.

mdorazio 10y ago

Yes, but they don't all die at the same time, so you can utilize a RAID or similar array to mitigate the failures at a small cost in total storage space. Ex. my 5-drive RAID array runs 5x 3TB drives and provides about 12TB of usable space. If any single drive fails, it's a quick swap with a cheap replacement. If I instead had a single 12TB drive fail, I'd be screwed. Even if I didn't have a RAID array, any single drive failure would be a maximum of 3TB lost, vs. losing everything with a single drive. Basically it's much easier to minimize your data loss risk profile if you spread your data across multiple drives instead of relying on a single drive. Of course, if you need 100TB+ of storage, you might as well put these new 16TB drives in an array and save on the controller costs.

zzalpha 10y ago
And then if there's an unrecoverable read error on one of those other massive drives during the rebuild, you're in deep trouble.. and the bigger the drive the more likely this is to happen (reaching near-certainty once the drive is large enough): http://www.zdnet.com/article/why-raid-5-stops-working-in-2009/ http://www.zdnet.com/article/why-raid-5-stops-working-in-200...
- snuxoll 10y ago
  Which is why the 3 and 4TB drives I have in my FreeNAS box at home are configured as mirrored pairs, the time it takes to resliver a drive in this configuration is already fairly long - RAID-Z or the hardware equivalent of RAID-5 would take upwards of days to complete and that's a disaster waiting to happen.
cmurf 10y ago
At this size, the rebuild time is a day, or even 2-3 days if it's actively being used during the rebuild. It still makes sense to do at least a 2x raid1, which rebuilds faster than a cluster over wired ethernet. But if you have this much online storage, you probably have a high availability need also, which implies cluster in case a storage brick loses a power supply or logic board. It's not just a drive that can fail.