Hi Jon, Thanks for the detailed response. It seems like specifically disabling software compression has helped quite a bit.
Greg On Sat, Jul 1, 2017 at 3:49 AM, Jon LaBadie <[email protected]> wrote: > 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 <[email protected]> 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 [email protected] > > > 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 [email protected] > 11226 South Shore Rd. (703) 787-0688 (H) > Reston, VA 20190 (703) 935-6720 (C) > -- Greg Dickie just a guy 514-983-5400
