detect shoe-shining

[Cass Witkowski]

How frequently does this happen? If you see it every 2-3 minutes or 5-6 minutes then it is the tape reversing. There are four tape bands on the tape each with 12 passes. So to fill a tape 48 passes are done on the tape.

[Cass Witkowski]

From the QS

Ultrium LTO-3 and the new LTO-4 tape drive features a breakthrough in recording technology by writing sixteen tracks simultaneously on a linear format of 704 tracks and 896 tracks (respectively).

896/16 = 56 passes on the tape.
1600 GB / 56 = 28.5 GB per pass
28000 MB / 107 MB/Sec = 261 seconds or 4.35 minutes

[RalfG]

Thanks for all your responses.

I'll try to get the SCSI log sense information next week.

The lib I we is an Overland Neo4100, I think it is identical to a MSL6000 lib. Watching the lib's display is no solution, because it's located in a datacenter.


Here's the network throughput (received on the backup server), dstat with a 2 seconds delay. The data is already highly compressed, mostly zip files. ~830 GB data per LTO-4 tape.

58M
10M
52M
95M
104M
90M
98M
60M
622k
71M
94M
88M
96M
93M
57M
937k
60M
94M
96M
88M
101M
60M
886k
60M
99M
96M
98M
90M
56M
849k
58M
96M
102M
104M
84M
56M
499k
72M
98M
92M
101M
81M
56M
2687k
90M
96M
89M
101M


There is a short dropout every 10-20 seconds.

The average performance I get from this backup running without spooling is : Bytes/sec=69,971,539. It seems that backing up direct over the net without spooling is faster, than despooling from a linux md raid1 device (despooling speed was ~60 MB/s).

[RalfG]

Here's the information about log page 34h:

sg_logs -p=34 /dev/sg6
HP Ultrium 4-SCSI B12H
No ascii information for page = 0x34, here is hex:
00 34 00 00 1e 00 00 60 02 00 00 00 01 60 02 00 d8
10 00 02 60 02 0a 50 00 03 60 02 00 ee 00 04 40 02
20 04 b0


sg_logs -h -p=34 /dev/sg4
HP Ultrium 4-SCSI B12H
Log page code=0x34, DS=0, SPF=0, page_len=0x1e
00 34 00 00 1e 00 00 60 02 00 01 00 01 60 02 00 00
10 00 02 60 02 0a 50 00 03 60 02 00 00 00 04 40 02
20 04 b0

[Tom O'Toole]

We are already up to B34W on the firmware, you must have a pretty early version, and should probably update that. Ours came with B23W, and I thought we had received a very early version of the drive.

[RalfG]

AFAIK Overland has not released a more recent fw yet for the Neo 4100 lib yet. And it's not possible to flash an other version.

[Curtis Ballard · Accepted solution]

The parameters in log page 34h have to
be interpreted with the operation that
just completed in mind. All parameters
are for the current tape, are for writes,
and are cleared at the start of a tape
load except for the native data rate which
is fixed. If the previous load didn't write much then the values can be deceptive.

Full decode from sg6 - kind of slow but
not showing shoe shining. I wonder if
this was a short read or write as I
would expect some repositioning at this
speed.

Header: 34 00 00 1e

Parameter: 00 00
Ignore this byte: 60
Parameter length: 02
Repositions per 100MB written: 00 00 << This is the shoeshine value

Parameter: 00 01
Ignore this byte: 60
Parameter length: 02
Data rate onto tape after compression in 100KB/s: 00 d8 == 216 -> 21.6 MB/s

Parameter: 00 02
Ignore this byte: 60
Parameter length: 02
Maximum Possible Data rate with this data in 100KB/s: 0a 50 == 2640 -> 264 MB/s

Paramter: 00 03
Ignore this byte: 60
Parameter length: 02
Rate of data into the drive in 100KB/s: 00 ee == 238 -> 23.8 MB/s

Parameter: 00 04
Ignore this byte: 40
Parameter length: 02
Native data rate with LTO-4 media in 100KB/s: 04 b0 == 1200 -> 120.0 MB/s

Pulling out just the shoeshine value
from sg4 1 reposition/100MB not bad at
all but the rest of the data doesn't
show any data written to tape at all so
the reposition value probably doesn't
mean much.

sg_logs -h -p=34 /dev/sg4
HP Ultrium 4-SCSI B12H
Log page code=0x34, DS=0, SPF=0, page_len=0x1e
00 34 00 00 1e 00 00 60 02 00 01 00 01 60 02 00 00
10 00 02 60 02 0a 50 00 03 60 02 00 00 00 04 40 02
20 04 b0

[RalfG]

Thanks for the detailed information! I'll check the numbers after the next backup and report back.

[RalfG]

Here are some results from last nights incremental backups, 2 jobs, only 23 GB data backed up.

Header:
34 00 00 1e

Repositions per 100MB:
00 00 60 02 00 01 -> 1

Data rate onto tape after compression in 100KB/s:
00 01 60 02 00 94 -> 1,48 MB/s

Maximum Possible Data rate with this data:
00 02 60 02 0a 50 -> 2640 -> 264 MB/s

Rate of data into the drive in 100KB/s:
00 03 60 02 02 f8 -> 76,0 MB/s

Native data rate with LTO-4 media:
00 04 40 02 04 b0 -> 120.0 MB/s


And the job results from the backup program:

#1
Job write elapsed time = 00:00:03, Transfer rate = 31.13 K bytes/second

#2
Job write elapsed time = 00:12:54, Transfer rate = 29.85 M bytes/second

I'm not sure how the data rate values from 34h and the backup program correspond.