Something strange stirs in the storage backwater swamps, long ribbons of rust that never forget At one end of the storage spectrum is fast and flashy SSD storage and at the other – still – is tape; streaming ribbons of rust that are cheaper and more reliable than disk, and still selling for on-premises and off-site archive data storage. Long-time tape library and drive supplier Quantum has brushed up its library offering …
Bit Error Rate (BER)
LTO-7 tape - Hard Error Rate 1 x 10 ^19 bits
Enterprise FC/SAS Hard Read Errors per Bits Read 1 sector per 1 x 10E^16 bits
Enterprise SATA Hard Read Errors per Bits Read 1 sector per 1 x 10E^15 bits
Desktop SATA Hard Read Errors per Bits Read 1 sector per 1 x 10E^14 bits
http://www.lto.org/wp-content/uploads/2014/07/LTO_Get_The_Facts_10_15.pdf
As as shop that did the move from tape to disk 6 years ago, I do confirm that the operational experience here is that disk is more reliable than tape. We no longer experience things like "not this backup, it's corrupted/incomplete/eaten by the dog, take the previous one", or wait hours to apply incremental dailies.
The BER issue (assuming there is one) it totally hidden by RAID 6 + replication.
As of cost, the whole driver for the project back then was cost reduction.
1) Individual tapes are more robust than individual drives, this is a fact. Read the Datasheets.
2) If you are experiencing problems with corrupt tapes you probably have an environmental problem like dust or vibration in your datacentre.
3) Incomplete backups is not a tape problem it is an operational problem. set up reporting on your tape library and backup software to identify any failed backups and get to the bottom of why they are happening.
4) Any cost model which shows disk to be cheaper than tape is likely to be flawed. There are some edge cases but they are rare in businesses of any size. there are benefits to using disk.
Disk has its place in data protection but so does tape and they are much stronger when used together.
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