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Re: hfs+ read only over fibre channel
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Re: hfs+ read only over fibre channel


  • Subject: Re: hfs+ read only over fibre channel
  • From: Brian Sturk <email@hidden>
  • Date: Mon, 02 Jul 2007 21:53:10 -0400

Mark Day wrote:
Probably the closest you can get is to do an update mount, with the MNT_RELOAD flag also set. Use at your own risk. Changing the on-disk structures behind the file system's back is very risky; you could corrupt the file system and lose data. This is not the right way to hook multiple machines up to a SAN.

-Mark
Hi Mark,

Thanks for the info. I'm pretty sure I've tried that although if I remember correctly I was attempting to use mount -o and reload (or was it update, can't recall) rather than doing it programmatically. I think what I ran into doing that was dealing with open file handles. I will play some more with that flag. I thought I recall reading somewhere that someone was able to accomplish this as of 10.4.6. Was anything added in 10.4.6 that might be relevant in this area? Maybe something in the IOMedia framework? I'll try and dig up where I read that.

And yep, I know just how *bad* this is (or can be). The machine I want to do the update on will be mounting read only so hopefully it won't actually corrupt the disk.

thanks again,
~brian

On Jul 2, 2007, at 3:51 PM, Brian Sturk wrote:

Not sure if this is the right mailing list for this sort of question.
If not I'll ask on the appropriate list.

I'm trying to force an HFS volume that is mounted read only to re-read
directory entries from disk (bypassing it's cache).  I haven't found
anything at the VFS layer that allows me to do that (cache_purgevfs
etc).   The VOP_READDIR path seems to go almost straight to the
underlying driver.  Just looking for any pointers on how to accomplish
this if it can even be done.  I know that re-mounting the volume
accomplishes this but I'm looking to do it *without* having to remount.

Having asked this I'm very aware of how dangerous this is i.e. reading
structures off the disk while another could be possibly writing to the disk.


Any info would be greatly appreciated!

~brian



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References: 
 >hfs+ read only over fibre channel (From: Brian Sturk <email@hidden>)
 >Re: hfs+ read only over fibre channel (From: Mark Day <email@hidden>)

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