[CentOS] iSCSI, windows, & local linux access

[Ross S. W. Walker]

> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of John R Pierce
> Sent: Friday, February 23, 2007 11:41 AM
> To: CentOS mailing list
> Subject: Re: [CentOS] iSCSI, windows, & local linux access
> 
> Andrew Cotter wrote:
> > Hello all,
> >
> > I am looking to build a larger array (6TB) using CentOS 4.4 
> to archive 
> > data to.  We want to have the Windows server mount this array as a 
> > local drive so we were looking at iSCSI to do it.  I have 
> played with 
> > it in the past and gotten it to work in this combo, but I have a 
> > question about access to the data on the local (Centos) machine.
> >
> > If I understand correctly, when I mount the device on 
> windows, I need 
> > to format the array in a format that Windows (2003 server) can 
> > understand.     Also, iSCSI only allows you to mount the 
> array on one 
> > server at a time.  Once I do that and write files to this array, is 
> > there anyway to access those files from the local machine 
> (Centos)?  I 
> > may want to do things like rsync to another location, copy files to 
> > another removable SATA disk, or just plain delete something.
> >
> > Is it a choice of the OS so both windows and linux can read it?  
> > Little help with which one then.  I know NTFS is still 
> somewhat in its 
> > infancy.
> 
> if its mounted as a block device, nothing else should touch 
> it, read OR 
> write.  block devices are NOT sharable, with the exception of 
> specialized filesystems like GFS or IBrix Fusion   Even a read only 
> access would have issues with metadata consistency, if windows is 
> updating a directory or MFT or whatever, linux could see stale/mixed 
> data and would just throw up

Technically yes, if the volume has long periods of no activity though
there should be no problem in taking a snapshot and mounting that.
Understand that if the volume is being actively used by a backup process
the data contained therein will not be consistent, but it will not harm
the production volume, just the snapshot will not be considered prime.

> the only 'safe' way to do it would be for the windows machine 
> to share 
> the logical file system, and have the linux system access it as a 
> smbmount via samba.
>    or use replication running on the windows server (rsync 
> from mingw, etc)

Yes sharing it and mounting it back via CIFS is more reliable for a
highly active volume, but if you plan to then copy-out data over the
network it will slow things down to a crawl.

> Windows 2003 server has its own snapshotting capabilities, btw.

Which IMHO are crap. If it's backup jobs that are accessed during a run,
but otherwise sit there unused, then you can snapshot them off LVM
fairly safely.

-Ross

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