15 Sep
2015
15 Sep
'15
11:35 a.m.
On Mon, Sep 14, 2015 at 4:56 PM, Richard Loken
<richardlo at admin.athabascau.ca> wrote:
These are LTO-5
cartridges that can hold up to 30 Tbyte of compressed data and it can be
written on the tape with astonishing speed.
That's one heck of a compression ratio, given that the native
(uncompressed) capacity of an LTO-5 cartridge is 1.5 TB. Usually the
vendors claim 2.5:1 compression, but obviously the actual compression
achieved is entirely dependent on the entropy of the data. I'd be
really surprised if the tape drive can stream at a high enough rate to
store 30 Tbyte; the native (uncompressed) streaming rate is 140 MB/s,
so for 20:1 compression it would have to transfer 2800 MB/s, which is
22 Gbit/s, more than even SAS or Fiber Channel can handle. With LTO
and similar tape drives, if you can't maintain streaming, the
performance goes to near zero, and you beat the heck out of the tape.