Hi Andy,
Is there a way to to enforce a read-only rule for particular data
servers? If this is possible, I can ensure that newly written data
avoids the systems that need to be "LVM'ed", while allowing the existing
data to be read. I am curious if I can replicate data under this
scenario using xrdcp, or will I still have to take the read-only systems
off-line to move the data?
I am concerned about the granularity of recovery actions in our systems
under LVM, but I need to support larger pathnames now. The pathnames
are being driven by the physics users and the use of metadata in the
path components.
Patrick
Andrew Hanushevsky wrote:
> Hi Patrick,
>
> You are quite right that the design of the cache does impose limits on
> file names. The oss was designed almost 10 years ago when there were no
> integrated LVM's and few that worked really well and users kept path
> names to less that 200 characters. Over the years, as LVM's became
> common, the oss turned into the "poor man's LVM". In general, we don't
> recommend using it if you have ready access to a suitable LVM. While,
> yes, you do give up some features (like fine-grained recoverability and
> application-directed partition selection) the other
> limitations may be even more annoying. We'll make sure that this
> restriction is prominently mentioned in the manual.
>
> The path you've chosen is about the only one that will work (i.e.,
> copying off the data and creating a single filesystem using an LVM).
>
> Now, we do have some ideas on how to remove the pathname length
> restriction but wonder if it's really worth the trouble of doing it,
> given that LVM's provide practically the same basic features. Any thoughts?
>
> Andy
>
> P.S. What's the driving force for very long path names at your site?
>
>
> On Sat, 1 Mar 2008, Patrick McGuigan wrote:
>
>> Hi,
>>
>> Some of our data servers have two disks and I am using the oss.cache
>> directive to use both disks to support a single namespace. However,
>> it looks like the users of our applications have already run into a
>> problem. All of the files are stored in one directory (for a single
>> cache) and the filename is the full namespace path with "/"
>> substituted with "%". Our problem arises from the fact that full
>> namespace path is now limited to the leafname length of the filesystem
>> (255 characters) when writing to the cache directory.
>>
>> I see a couple of ways to mediate the problem; removing one disk or
>> using and LVM to create one drive in the OS. I am curious if there
>> are other alternatives?
>>
>> If I have to move to one disk, I would like to migrate the data in the
>> existing caches to other data servers while I rework the existing
>> system. What is the best way to migrate this data? I am planning on
>> taking the "problem" data server off-line and use xrdcp to move the
>> data to the other servers.
>>
>> Regards,
>>
>> Patrick
>>
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