[gpfsug-discuss] Mass UID migration suggestions

[Jez Tucker]

Perhaps IBM might consider letting you commit it to 
https://github.com/gpfsug/gpfsug-tools he says, asking out loud... It'll 
require a friendly IBMer to take the reins up for you.  Scott? :-)

Jez


On 03/08/17 02:00, Aaron Knister wrote:
> I'm a little late to the party here but I thought I'd share our recent 
> experiences.
>
> We recently completed a mass UID number migration (half a billion 
> inodes) and developed two tools ("luke filewalker" and the 
> "mmilleniumfacl") to get the job done. Both luke filewalker and the 
> mmilleniumfacl are based heavily on the code in 
> /usr/lpp/mmfs/samples/util/tsreaddir.c and 
> /usr/lpp/mmfs/samples/util/tsinode.c.
>
> luke filewalker targets traditional POSIX permissions whereas 
> mmilleniumfacl targets posix ACLs. Both tools traverse the filesystem 
> in parallel and both but particularly the 2nd, are extremely I/O 
> intensive on your metadata disks.
>
> The gist of luke filewalker is to scan the inode structures using the 
> gpfs APIs and populate a mapping of inode number to gid and uid 
> number. It then walks the filesystem in parallel using the APIs, looks 
> up the inode number in an in-memory hash, and if appropriate changes 
> ownership using the chown() API.
>
> The mmilleniumfacl doesn't have the luxury of scanning for POSIX ACLs 
> using the GPFS inode API so it walks the filesystem and reads the ACL 
> of any and every file, updating the ACL entries as appropriate.
>
> I'm going to see if I can share the source code for both tools, 
> although I don't know if I can post it here since it modified existing 
> IBM source code. Could someone from IBM chime in here? If I were to 
> send the code to IBM could they publish it perhaps on the wiki?
>
> -Aaron
>
> On 6/30/17 11:20 AM, hpc-luke at uconn.edu wrote:
>> Hello,
>>
>>     We're trying to change most of our users uids, is there a clean 
>> way to
>> migrate all of one users files with say `mmapplypolicy`? We have to 
>> change the
>> owner of around 273539588 files, and my estimates for runtime are 
>> around 6 days.
>>
>>     What we've been doing is indexing all of the files and splitting 
>> them up by
>> owner which takes around an hour, and then we were locking the user 
>> out while we
>> chown their files. I made it multi threaded as it weirdly gave a 10% 
>> speedup
>> despite my expectation that multi threading access from a single node 
>> would not
>> give any speedup.
>>
>>     Generally I'm looking for advice on how to make the chowning 
>> faster. Would
>> spreading the chowning processes over multiple nodes improve 
>> performance? Should
>> I not stat the files before running lchown on them, since lchown 
>> checks the file
>> before changing it? I saw mention of inodescan(), in an old gpfsug 
>> email, which
>> speeds up disk read access, by not guaranteeing that the data is up 
>> to date. We
>> have a maintenance day coming up where all users will be locked out, 
>> so the file
>> handles(?) from GPFS's perspective will not be able to go stale. Is 
>> there a
>> function with similar constraints to inodescan that I can use to 
>> speed up this
>> process?
>>
>> Thank you for your time,
>>
>> Luke
>> Storrs-HPC
>> University of Connecticut
>> _______________________________________________
>> gpfsug-discuss mailing list
>> gpfsug-discuss at spectrumscale.org
>> http://gpfsug.org/mailman/listinfo/gpfsug-discuss
>>
>

-- 
*Jez Tucker*
Head of Research and Development, Pixit Media
07764193820 | jtucker at pixitmedia.com <mailto:jtucker at pixitmedia.com>
www.pixitmedia.com <http://www.pixitmedia.com> | Tw:@pixitmedia.com 
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