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тАО03-13-2008 01:41 PM
тАО03-13-2008 01:41 PM
I'm backing up large amounts of data to a lib with 2 LTO-4 drives. Because of the long time the backup takes to complete, I don't want to spool the data to disk and then write to tape for full backups.
The disk storage (file server) has a seq. read performance of 200-300 MB/s and is connected by GbE to the backup server.
The data are mainly large files.
The following is the output of dstat on the file server during a full backup with spooling enabled.
--dsk/sde-- --net/eth1-
read _writ|_recv _send
104M 0 |2509k 105M
104M 0 |2541k 106M
104M 0 |2536k 106M
72M 0 |2032k 85M
0 0 | 12k 1848k
58M 0 |1035k 42M
102M 0 |2527k 105M
106M 0 |2558k 107M
104M 0 |2543k 106M
107M 0 |2548k 106M
106M 0 |2558k 107M
106M 0 |2555k 107M
104M 0 |2558k 107M
16M 0 |1413k 60M
0 0 | 11k 1313k
0 0 | 70B 70B
64M 0 | 295k 12M
104M 0 |2555k 107M
It looks similar without spooling. I'm not sure what the reason for the short dropouts is.
I'm a bit worried about tape shoe-shining without spooling and want to know if there is a way to get the status about how often a drive had to start/stop during a full backup (scsi command, ltt...).
Solved! Go to Solution.
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тАО03-13-2008 01:57 PM
тАО03-13-2008 01:57 PM
Re: detect shoe-shining
So in-short - don't worry about it.
HTH
Duncan
I am an HPE Employee
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тАО03-13-2008 02:11 PM
тАО03-13-2008 02:11 PM
Re: detect shoe-shining
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тАО03-14-2008 01:18 AM
тАО03-14-2008 01:18 AM
Re: detect shoe-shining
You can also test (with LTT) where the problem is:
In LTT there are several performance test available: system performance and device performance.
first use the device perfomance, this test will generate data in the host memory and send it to the LTO drive, this will give you some indication about the scsi subsystem, yo should be able to reach the teorical tape throughput
then you have the system perfomance, here you can test the the source of the data, and have an idea of the max throughput your system can deliver, you can also create a fixed amount of data (this is the restore test) and then test the system with those data, and this will give you an idea if your problem is comming form the HW or from data (defragmented, openfiles, antivirus....)
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тАО03-14-2008 01:47 AM
тАО03-14-2008 01:47 AM
Re: detect shoe-shining
With dd and the other tests, I get read/write performance up to 190 MB/s.
The problem is, I don't know if there are periods during a backup with an average throughput of 70 MB/s, where the throughput drops below 40 MB/s. I can see with dstat that there are periods where the the network throughput between file server and backup server drops to <10 MB/s, but I don't know if the drive starts shoe-shining then.
If this happens only a few times during a long running backup, it'd be fine. But if this happens often, I'm worried about the additional stress for the tape and drive.
Hence I would like to see some number on how many time the drive had to stop/rewind/start during a given time.
Maybe I'm too afraid about this. But sometimes people forget to put the data in gzip format on the file server, the result is many very small files...
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тАО03-14-2008 06:05 AM
тАО03-14-2008 06:05 AM
Re: detect shoe-shining
see example:
|__ Mechanism EEPROM Page
||__ Power on time : 109243379
||__ Power cycles : 88
||__ Tape pulled : 30012154
||__ Pulling time : 12134187
||__ Load/unloads : 1595
||__ Start/stops : 1295420
||__ Thread cycles : 3537
||__ Repositions : 7032
||__ Turnarounds : 1219383
||__ SDRAM errors : 1
||__ CRC errors : 0
||__ Cleanings : 16
||__ Upgrades : 3
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тАО03-14-2008 07:15 AM
тАО03-14-2008 07:15 AM
Re: detect shoe-shining
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тАО03-14-2008 12:06 PM
тАО03-14-2008 12:06 PM
Re: detect shoe-shining
There are two things that happen with Shoe-Shining.
1) Extra mechanical wear
2) Performance impact
With HP LTO tapes and drives both the drive and the tape cartridge are extensively tested and required to meet standards where the extra mechanical wear isn't an issue. You will get the rated life in worst case operation.
2) Performance impact
Here HP's LTO tape drives really shine. We have the variable rate matching which isn't available in some other LTO tape drives. With variable rate matching the tape drive will slow down as the data rate slows down up to 1/3 of the max speed. The drive input buffer is designed such that at 1/3 of the max speed the buffer is large enough to hold all of the data that can come in during a reposition. That means that the drive can always write the data at the speed it arrives. Something not every LTO drive can do.
The specific log page you will need if you want to see the reposition information is 34h. If you have a way to issue the SCSI Log Sense command and get back a log page 34h I can provide the information on what field has the reposition information.
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тАО03-14-2008 03:45 PM
тАО03-14-2008 03:45 PM
Re: detect shoe-shining
What kind of library do you have. On the MSL5000/6000 series, it tells you what it's doing on the front panel status display. You can spot possible shoe-shining if it's changing from writing... to idle... repeatedly.
It seems like the breaks you are seeing could just be an artifact of buffering on the host file system, and maybe your samples are too frequent to smooth these out. You don't say what the interval is.
Assuming this is linux, you could maybe try piping through the 'buffer' program and see how that goes.
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тАО03-14-2008 04:40 PM
тАО03-14-2008 04:40 PM