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тАО08-26-2004 02:08 AM
тАО08-26-2004 02:08 AM
The purpoce of the exercise:
1) Tape & streamer failures does happen.
2) 1-st copy send offsite (Disaster) 2-nd copy store local in my hands.
I am thinking of:
#vdump -f - /usr | tee /dev/ntape/tape0_d1
> /dev/ntape/tape1_d1
If anybody tried such dirty tricks?
Solved! Go to Solution.
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тАО08-26-2004 07:57 AM
тАО08-26-2004 07:57 AM
Re: vdump to two tapes
interesting idea. Read once, write twice. I am going to test it. For good performance the two tapes should be connected to different controllers.
greetings,
Michael
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тАО08-26-2004 02:43 PM
тАО08-26-2004 02:43 PM
SolutionTried it.
Had problems got an I/O error on the second run.
Tried the same with an advfs clone, works a charm.
ie.
clonefset usr_dmn usr_fset clone_usr_fset
then
mount -t advfs usr_dmn#clone_usr_fset /clone_usr
vdump -f - /clone_usr | tee /dev/ntape/tape0_d1 >/dev/ntape/tape2_d1
Restore works fine!!
Regards,
Orrin.
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тАО08-26-2004 10:22 PM
тАО08-26-2004 10:22 PM
Re: vdump to two tapes
vdump normally reads/writes with 64k blocksize on tape. I don't know what blocksize tee
Why not simply starting 2 times vdump ?
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тАО08-26-2004 11:50 PM
тАО08-26-2004 11:50 PM
Re: vdump to two tapes
Why not simply starting 2 times vdump ?
Because they won't be identical and would use twice the resources in regard to cpu and disk I/O.
Michael
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тАО08-27-2004 05:56 AM
тАО08-27-2004 05:56 AM
Re: vdump to two tapes
I do not have two stareamers on hands currently to test it. But streamers are cheap.
Unfortunately, I cannot afford two separate SCSI controllers ;-(( - No PCI slots left.
However, system reads from disk @ 20 MB\sec,
and SDLT320 device has 40 MB\s bus.
I hope it will be OK.
Orrin, Thank You very much for Your opinion!
I do not have advfs utilities licence, but probably HP will sell me one.
Erich Wimmer, thank You for 8-kb block size standard output limitation!
Maybe,
| tee
will do the trick? According to man, tee can do up to 20 output files - looks enough :-)!
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тАО08-27-2004 07:39 AM
тАО08-27-2004 07:39 AM
Re: vdump to two tapes
I am still planning to test your command as soon as I have couple of drives available.
Btw, another idea to make a clone tape, may be use 'tcopy' to make a clone copy of the tape created by a regular vdump..
regds,
Abdul.
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тАО08-29-2004 07:54 PM
тАО08-29-2004 07:54 PM
Re: vdump to two tapes
looking deeper into tee it looks like the following:
The maximum buffer size within tee is 8k/bytes, writes are using the same record size as read() returns. So you will never get more than 8k records, also if using
"tee /dev/ntape/tape1 |dd of=/dev/ntape/tape2 obs=256k", but tape1 gets only 8k at maximum. 8k tape blocks are wasting space on tape and increases the backuptime exponential. Therefore "tee" is not applicable for tape backups.
You will see this behavior if tracing the read() write() systemcalls.
Greetings, Erich.
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тАО09-05-2004 10:35 PM
тАО09-05-2004 10:35 PM
Re: vdump to two tapes
Let's hope HP will increase the buffer in future releases - this looks like not very difficult task.
I expect to have streamer soon and have a look at this.
One more question:
if one of two streamers will fail during backup, will vdump|tee continue or stop?
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тАО09-06-2004 04:30 AM
тАО09-06-2004 04:30 AM
Re: vdump to two tapes
I believe vdump|tee continues but:
the tape driver makes x retries if the block cannot be written, then tee will be notified about a write error, tee writes the next block in sequence (so the defective block has been lost) and so on. If from this position on the tape is defective to the end, you have no chance to change the tape media, except killing the whole backup.
Greetings, Erich