DOA Hard Drive

Gdetrailer wrote:

rlw999 wrote:

philh wrote:
First time I've ever had a hard drive DOA. Was upgrading drives in my home server, as the drives were a bit old and wanted to increase space. Five years ago, said I'll never run out of space, LOL. Four 8TB raid 5 should be good for awhile!

Large RAID-5 arrays take a long time (a day, or multiple days) to resilver after a disk loss, and if you lose another disk during the rebuild, you'll lose the entire array. Rebuilding itself stresses the disks making a multi-disk failure not uncommon.

Have worked with RAID systems on servers since the 1990s and what you posted isn't really true on good quality RAID systems.

Good quality dedicated hardware based RAID controllers have their own processor and on board buffer memory with a backup battery and handles rebuilds in the background and you never see any data loss with RAID5 unless you lose more than 1 drive at a time, perhaps might see a slight reduction in array speed while array has be degraded.

Didn't you just say the same thing as me but you took the optimistic view?

I said that with RAID-5 if you lose another drive during the rebuild, you'll lose the entire array, you said that if you don't lose another drive during the rebuild, you won't lose any data.

Whether you have hardware RAID or not, resilvering 24TB of data is going to take days, maybe over a week. And during that time the disks are going to be 100% busy so if any of the other ones were near failure, that's when they are going to fail.

Back when "large" drives were 150GB SAS drives that could sustain 200MB/sec (with a deep 254 entry command queue), rebuilds happened relatively quickly and a hot spare could save the day. But throughput hasn't kept up with capacity increases, now you can get 8TB drives (50X larger) and you're luck if you can sustain 150MB/second. Just reading 8TB at 150MB/second takes 14 hours, but when you're rebuilding a RAID array you're reading and writing at the same time, so throughput drops.

Best to avoid software based RAID, just not robust or fast once you see the difference between a dedicated Hardware based RAID.

I run ZFS RAID-Z2 (which is close to software RAID-6) and one nice advantage is that when it has to resilver the array, it knows which blocks have data so it only needs to rebuild parity for that data, so if I'm only using 1T out of 8TB, that's all it needs to rebuild.