> 15 km/h
The tape stores 580TB for a length of 1255m, does that mean the read speed is 580TB/1255m*15km/h = 1.9TB/s ? Seems too high.
The tape stores 580TB for a length of 1255m, does that mean the read speed is 580TB/1255m*15km/h = 1.9TB/s ? Seems too high.
The drive has 32 heads, and reads/writes 32 tracks at a time. It goes from the start of the tape to the end, then aligns with the next 32 tracks and reverses direction.
Each group of 32 tracks is called a wrap. There are 208 wraps, so 6656 total data tracks. Even wraps go one direction, and odd wraps go the other direction.
That's the important part.
But also the tape is divided into 4 "bands", each one holding a quarter of the wraps/tracks. Between the bands, and at the edges of the tape, are special servo tracks that are used for alignment.
So when a source talks about "wraps per band", it's pointless abstraction. Unless you're really in the weeds, the only thing you want to know is the total number of wraps.
It did say that. I wonder if there's some multi-track/double-layer/double-sided stuff going on that needs multiple passes to read, that does sound awful fast!
Also, I suppose they limit the read bandwidth with something like what a single Infiniband connection would support; few disk arrays support much higher speeds.
You could hypothetically do that, for sure, but the software basically is derived from the tape era where you'd just have one logical stream coming out of the tape.
The numbers they cite for "previous generations" don't match up to the progression of the LTO tape series' capacity. Maybe they are citing "research numbers" that they can do in a lab but aren't production-ready yet. I would certainly assume they are citing "compressed" data figured there.
Also bear in mind that tapes typically store data striped across the tape in multiple tracks and multiple bands. There are four bands per tape and 12-52 wraps per band, so reading the whole tape requires up to 208 passes across the tape.
https://en.wikipedia.org/wiki/Linear_Tape-Open#Physical_stru...
But yes, to agree with another parallel comment, tape data rates are quite high sequentially (abysmal in random of course, but that's not how they're used). LTO-8 does 750 megabytes per second compressed / 360 megabytes per second raw.