On Fri, Jun 30, 2017 at 06:47:57PM -0400, Greg Dickie wrote:
> Hi Jon,
>
> I did. I gave me this:
> define tapetype IBM-LTO7 {
> comment "Created by amtapetype; compression disabled"
> length 5876531200 kbytes
> filemark 4964 kbytes
> speed 291436 kps
> blocksize 2048 kbytes
> }
>
> The drive is SAS connected on a 6G HBA. I'm not sure what units kps is.
>
KiloBytes / Second
So you are able to feed the drive from memory at 290 MB/s,
close to its rates 300.
Of course, during a backup without a holding disk, you may
lose speed in reading from disk, transferring over the network,
etc.
LTO drives are designed to stream (run at a constant speed).
Typically they can stream at two speeds, maximum (300MB/s
in your case) and half-maximum. The drives contain considerable
memory to buffer the data feed which could vary in rate or be
insufficient to maintain streaming.
When the data feed is insufficient, the drive waits for the
buffer to fill to some level, starts the tape, when up to
speed writes from the buffer until it drops to some level.
The drive stops writing, slows the tape to a stop, reverses
the tape to before where it last wrote and stops. When the
buffer fills again, this cycle of start/write/stop/reverse
repeats. This undesireable behavior is called "shoe-shining".
One result is very low write speeds.
While a holding disk is not appropriate in all cases one
purpose of a holding disk is to provide a consistant,
high speed data source for feeding the tape drive.
Jon
>
> On Fri, Jun 30, 2017 at 5:18 PM, Jon LaBadie <j...@jgcomp.com> wrote:
>
> > On Fri, Jun 30, 2017 at 03:30:19PM -0400, Greg Dickie wrote:
> > > Hi Alan,
> > >
> > > Thanks for the response. It looks to me like taper is slow. I'm trying
> > to
> > > not use a holding disk, the NAS is 250TB and doesn't make sense to have
> > > 250TB locally to cache it. It's connected by a 10G ethernet connection
> > so I
> > > "should" be able to stream pretty quickly from it. i did put a 1TB disk
> > as
> > > a part cache but that seemed to behave the same way.
> > >
> > Have you run amtapetype to see what speed
> > you might expect as a maximum?
> >
> > Admins have often had great difficulty getting
> > LTO drives to run at rated speed.
> >
> > jl
> > --
> > Jon H. LaBadie j...@jgcomp.com
> > 11226 South Shore Rd. (703) 787-0688 (H)
> > Reston, VA 20190 (703) 935-6720 (C)
> >
>
>
>
> --
>
>
> Greg Dickie
> just a guy
> 514-983-5400
>>> End of included message <<<
--
Jon H. LaBadie j...@jgcomp.com
11226 South Shore Rd. (703) 787-0688 (H)
Reston, VA 20190 (703) 935-6720 (C)
