[Gluster-devel] 3.6.1 issue

[Joe Julian]

Or get tar to change their behavior?

On December 21, 2014 9:40:08 AM PST, "David F. Robinson" <david.robinson at corvidtec.com> wrote:
>So for now it is up to all of the individual users to know they cannot
>use tar without the -P switch if they are accessing a data storage
>system that uses gluster? 
>
>David  (Sent from mobile)
>
>===============================
>David F. Robinson, Ph.D. 
>President - Corvid Technologies
>704.799.6944 x101 [office]
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>David.Robinson at corvidtec.com
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>
>> On Dec 21, 2014, at 12:30 PM, Vijay Bellur <vbellur at redhat.com>
>wrote:
>> 
>>> On 12/20/2014 12:09 PM, David F. Robinson wrote:
>>> Seems to work with "-xPf".  I obviously couldn't check all of the
>files,
>>> but the two specific ones that I noted in my original email do not
>show
>>> any problems when using -P...
>> 
>> This is related to the way tar extracts symbolic links by default &
>its interaction with GlusterFS. In a nutshell the following steps are
>involved in creation of symbolic links on the destination:
>> 
>> a) Create an empty regular placeholder file with permission bits set
>to 0 and the name being that of the symlink source file.
>> 
>> b) Record the device, inode numbers and the mtime of the placeholder
>file through stat.
>> 
>> c) After the first pass of extraction is complete, there is a second
>pass involved to set right symbolic links. In this phase a stat is
>performed on the placeholder file. If all attributes recorded in b) are
>in sync with the latest information from stat buf, only then the
>placeholder is unlinked and a new symbolic link is created. If any
>attribute is out of sync, the unlink and creation of symbolic link do
>not happen.
>> 
>> In the case of replicated GlusterFS volumes, the mtimes can vary
>across nodes during the creation of placeholder files. If the stat
>calls in steps b) and c) land on different nodes, then there is a very
>good likelihood that tar would skip creation of symbolic links and
>leave behind the placeholder files.
>> 
>> A little more detail about this particular implementation behavior of
>symlinks for tar can be found at [1].
>> 
>> To overcome this behavior, we can make use of the P switch with tar
>command during extraction which will create the link file directly and
>not go ahead with the above set of steps.
>> 
>> Keeping timestamps in sync across the cluster will help to an extent
>in preventing this situation. There are ongoing refinements in
>replicate's selection of read-child which will help in addressing this
>problem.
>> 
>> -Vijay
>> 
>> [1] http://lists.debian.org/debian-user/2003/03/msg03249.html
>> 
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-- 
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