Is software verification necessary with LTO drives?

[theboyk]

While testing Retrospect 9 performance with a couple of my LTO-4 drives, I was skimming the wiki page for LTO technology and came across this bit of information:

 

"LTO uses an automatic verify-after-write technology to immediately check the data as it is being written, but some backup systems explicitly perform a completely separate tape reading operation to verify the tape was written correctly. This separate verify operation doubles the number of end-to-end passes for each scheduled backup, and reduces the tape life by half."

 

and then later in the article, it again states:

 

"The tape drives use a strong error correction algorithm that makes data recovery possible when lost data is within one track. Also, when data is written to the tape it is verified by reading it back using the read heads that are positioned just 'behind' the write heads. This allows the drive to write a second copy of any data that fails the verify without the help of the host system."

 

I'm wondering if enabling Retrospect-based verification is a redundant process? Is the drives automatic verify-after-write technology enough or is Retrospect's verification still required? If I don't need to have Retrospect verify the process, it will not only decrease the wear & tear on the drive and tapes, but it'll also cut down the time required to run a backup by half (which would be great).

 

So, would love to hear people's opinions on this?

 

Thanks,

Kristin.

[prl]

The error correction used is probably some sort of Reed-Solomon code. Which can detect and repair up to a certain fixed number of error bits per block (and detect but not fix somewhat more). The number of bits that can be fixed is a function of the number of error-correction bits added to the data. "Strong" doesn't really cut it as a measure of how good an ECC is. Block size, ECC size and algorithm is.

 

DVDs also have ECC. But I still sometimes get errors when I check them, However, DVDs are also subject to prl's law of storage media reliability: Never trust storage media you can put your fingers on

[theboyk]

Thanks for the reply. Spoke to the drive manufacturer and they said that while the error detection should be enough, if you can afford the extra wear & tear of the hardware and tapes, it's worth it for the peace of mind.

 

So, in my case, as we only use our tapes for a single cycle (usually lasting a couple months), then send a redundant pair into storage, we can afford the wear & tear of the verification process.

 

Thanks again,

Kristin.