LTO6 and ATS / Data Rate Matching

[andre80]

Good Day

I'm in an project where we want to replace our nearly 6 Years old LTO4 MSL4048 Library with a new one with LTO6 Tape Drives.

Some Years ago i had a discussion with a guy from the hp labs about the Data Rate Matching for LTO4 which is from 40-120MB/s (depending on LTO4 Drive). He told me then, it is not critical to go under those 40MB/s... Lto could handle speeds well even if they are under 10MB/s. In the last several years i never had problems with lto4 tapes and lower speed  for example under 10 or 20 MB/s. It does result in a slower backup but never had problems with tapes or drives...

how about LTO6, is there really a need to run  D2D2T Backup design? I've seen that the Data Rate from LTO6 starts from 54MB/s. Has anyone experience about that with lto6.

thanks

[Tom L]

Andre,

All drives have a min/max throughput characteristic when it comes to "streaming" data to the drives.  HP Specifications shows 54mb/sec as the minimum, 160mb/sec maximum.  This is coined as Adaptive Tape Speed and allows the reels to slow down/speed up as needed.

Whenever the drive buffer empties and the drive can no longer write data, it must stop, rewind, and wait for the buffer to fill before going on.  If data cannot be streamed to at least 54mb/sec, the drive will do this over and over, stopping rewinding, writing, repeat.  This is called "shoe-shining" and causes excessive wear on both the drive and the media and should be avoided if at all possible.

So can the drive work at 10mb/sec?  Yes, but it's not an optimal configuration.  Do what you can to increase the bandwidth of the data to the drive.

[andre80]

Hi Tom

Thanks for your reply. I got those speed ranges in mind. In know back to lto3 or lto4 days people say it does destroy tape mechanism and media if you go under the recommended speed ranges. I can say i never did face issues, but i'm curious if the statement is still true nowadays...

regards

andre

[Torsten.]

Grep the document for

"Data rate matching range":

http://h18000.www1.hp.com/products/quickspecs/13572_div/13572_div.PDF

LTO-4 40-120 MB/s
LTO-5 47-140 MB/s
LTO-6 54-160 MB/s

[andre80]

Hi Torsten

Thanks for your reply. i had a look at the paper and found this interessting statement (red makred)

Data Rate Matching Data Rate Matching combines sophisticated buffer management with HP's exclusive Variable Adaptive

Tape Speed technology to allow the tape drive to match its transfer rate to the host speed dynamically

and continuously across the wide range of transfer rates. This feature ensures that the tape drive

continues to stream data regardless of the environment, and brings two big advantages:

It optimizes backup performance, regardless of the speed of the host or the network

It minimizes rewinding and repositioning of the tape, reducing wear and increasing reliability

-> so if i get it right, it does not really matter how fast i can deliver data to the tape device? so it should be no problemen even i don't get into the adaptive speed range from 54-160MB/s?

regards

andré

[Torsten. · Accepted solution]

You need to deliver data in this range, otherwise the drive will start shoe shining ... IMHO the statement means you don't need to deliver with full speed.