[gpfsug-discuss] default inode size

[Jan-Frode Myklebust]

Another thing to consider is how many disk block pointers you have room for
in the inode, and when you'll need to add additional indirect blocks. Ref:
http://files.gpfsug.org/presentations/2016/south-bank/
D2_P2_A_spectrum_scale_metadata_dark_V2a.pdf

If I understand that presentation correctly.. a block pointer is 12 bytes,
so a 1 KB inode can hold approximately 70 block pointers -- ie. any file
larger than 70 blocks will need additional indirect blocks to hold the
addresses, requiring minimum one additional sub-block. With a 1 MB
blocksize filesystem (data and metadata), files between 75 MB and 3 GB will
need 1x inode and 1x indirect block = 1 KB + 32 KB metadata space. If your
files are smaller than 75 MB, the address pointers fit in the 1K inode.

If you have 4 KB inode, files smaller than 340 MB will fit all pointers in
the inode.


  -jf


On Wed, Mar 15, 2017 at 2:26 PM, Lukas Hejtmanek <xhejtman at ics.muni.cz>
wrote:

> On Wed, Mar 15, 2017 at 01:12:44PM +0000, GORECKI, DIETER wrote:
> > One other thing to consider is the storage of data inside the inode
> itself for very small files. GPFS has the ability to use the remaining
> [kilo]bytes of the inode to store the data of the file whenever the file is
> small enough to fit in.
> >
> > Anyone correct me if I am wrong, but with 4k inodes, you can store up to
> (4096-128 header) 3968 bytes of data. (without ILM)
> >
> > So regarding the size of the files you intend to store into your
> filesystem, it might be very interesting to take advantage of the
> performance of your SSD's to store small files.
>
> I agree it would, however, I have 30 % free capacity on SSDs only right
> now (with
> some snapshots and ~70M files). So I'm afraid I have to either change the
> rotational disks to hold metadata as well or do not create more
> files/snapshots or decrease the inode size. I cannot add more SSDs as I do
> not
> have free disk slots in HW.
>
> --
> Lukáš Hejtmánek
> _______________________________________________
> gpfsug-discuss mailing list
> gpfsug-discuss at spectrumscale.org
> http://gpfsug.org/mailman/listinfo/gpfsug-discuss
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://gpfsug.org/pipermail/gpfsug-discuss_gpfsug.org/attachments/20170315/b395e754/attachment-0002.htm>