[Lustre-discuss] FIDs and client side 64 bit inodes

Tue Feb 3 14:55:05 PST 2015

Thanks Andreas,

Since it is possible, although rare to have two valid FIDs
map to the same inode, I'll keep that in mind ;)

Kris

On 1/31/15 12:21 AM, Dilger, Andreas wrote:
> The similarity between FIDs and inode numbers is intentional, but FIDs are 128 bits (96 bits of you ignore the unused f_ver for now) while inode numbers are only 64 bits (or 32 on 32-bit CPUs).
>
> The mapping of FIDs to inode numbers will not overlap for a long time, but eventually there would be duplicates if the filesystem is used long enough and/or is very large (lots of MDTs and OSTs and clients).
>
> The FIDs themselves will never be reused, so they will always be unique for each file. The inode numbers are not strictly guaranteed to be unique, but due to the long period between FIDs that map to the same inode, the chance of 64-bit inode number collisions is very small. The chance of collisions on 32-bit apps/CPUs is much higher, and guaranteed for large filesystems with more than 4B inodes (though it would likely be hit earlier).
>
> Cheers, Andreas
>
>> On Jan 30, 2015, at 16:25, Kristen J. Webb <kwebb at teradactyl.com> wrote:
>>
>> Here is my current lustre version for testing:
>>
>> # cat /proc/fs/lustre/version
>> lustre: 2.6.92
>> kernel: patchless_client
>>
>> I've noticed that my changelog records look a lot like generated inodes.  From a changelog entry:
>>
>>     [0x200000bd2:0x13a:0x0]
>>
>> And from ls -i on a lustre client:
>>
>>     144115238843711802 (0x200000BD200013A)
>>
>> This is nice, if I split the inode number into the sequence and oid numbers (ignoring the version for now) I can use this in calls like
>>
>>     lfs fid2path
>>
>> Will I always be able to do this with 64 bit inodes that I get with calls like ls -i on a lustre client?
>>
>> If not, then is it accurate to say that at any point in time, for each unique file in a lustre file system, there is only one FID=[seq:oid:ver] that can be used to generate a unique 64 bit inode for clients (even if the value of the inode does not map backwards like the example above)?
>>
>>
>> Kris
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This message is NOT encrypted
--------------------------------
Mr. Kristen J. Webb
Chief Technology Officer
Teradactyl LLC.
2450 Baylor Dr. S.E.
Albuquerque, New Mexico 87106
Phone: 1-505-338-6000
Email: kwebb at teradactyl.com
Web: http://www.teradactyl.com

Providers of Scalable Backup Solutions
    for Unique Data Environments

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Regular internet e-mail transmission cannot be guaranteed to be secure or 
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