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akshar bhosale
how to know where file is getting written
on May 15, 2011 at 5:49:32 am

hi,

we have san storage with dm multipath. Now we want to know when we write any file, on which device it is getting written? from filesystem end, we are not able to know as to on which msa (physical device) it is getting written.

-akshar


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Chris Gordon
Re: how to know where file is getting written
on May 15, 2011 at 5:12:13 pm

Can you describe your setup a little bit more? What hardware and software are you using? What is the configuration?


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akshar bhosale
Re: how to know where file is getting written
on May 16, 2011 at 4:50:54 am

Hi,
we have 8 no of HP p2000 and each is having 3 more jbods attached to it. MSAs are connected with file serving nodes through fc SAn. We have x9000 ibrix file system. 8 file serving nodes are also connected using fc san.


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Chris Gordon
Re: how to know where file is getting written
on May 16, 2011 at 11:07:23 am

The answer to your question -- exactly where something is written -- is going to be very vendor specific. You need to contact HP and discuss that with them or find some IBRIX forums/groups and ask there. This is far from a generic SAN or generic storage question.


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akshar bhosale
Re: how to know where file is getting written
on May 16, 2011 at 7:14:55 pm

thanks.. i really have 2 log the case..thank you once again..


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Jason Myres
Re: how to know where file is getting written
on May 16, 2011 at 5:21:18 pm

[akshar bhosale] "on which device it is getting written?"

Short answer: all of them.

Long Answer: I took a quick look at an IBRIX white paper, and it seems to be a lot like other shared disk file systems, where the "Segment Servers" are equivalent to the Metadata Controllers used in a StorNext or Xsan environment.

Assuming that's correct, then your arrays (MSAs) have been gathered into storage pools that are striped together to form your SAN volume. When files are copied to the volume, the individual blocks of data that make up those files are written across all of the arrays at once.

There are ways to control this using affinities, or by creating separate volumes for different types of data, but you would have to look into how your SAN is configured to see if anything like that has been set up. If you need to remove or re-purpose some of your arrays, many SAN filesystems have data migration features that allow you to re-assign blocks to the arrays you want to keep, so you can de-commission the arrays you need to remove.

JM


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Steve Modica
Re: how to know where file is getting written
on Jun 3, 2011 at 12:13:56 am

In the iSCSI or FCoE world, we would tell using:

sar -n DEV 2 100

This samples 2 seconds at a time (100 times) and outputs the per second average IO over each port. (You run this in a terminal)

This won't work for FC stuff since they aren't ethernet (They are EtherNOT!!!)

If your FC drivers came with utilities, you might find some way using one of those.

Steve Modica
CTO, Small Tree Communications


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Steve Modica
Re: how to know where file is getting written
on Jun 3, 2011 at 11:45:37 pm

fs_usage might show you the device file. (It does not show that on my system, but I don't have FC drivers installed)

Steve Modica
CTO, Small Tree Communications


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