Re: UFS2 max limits?

From: John-Mark Gurney (gurney_j_at_resnet.uoregon.edu)
Date: 11/13/05

  • Next message: John-Mark Gurney: "Re: UFS2 max limits?" 
    Date: Sun, 13 Nov 2005 10:17:59 -0800
To: Joseph Koshy <joseph.koshy@gmail.com>

    Joseph Koshy wrote this message on Sat, Nov 12, 2005 at 11:05 +0530:
    > The Wikipedia page referenced below says that UFS2 supports a
    > filesystem size of 2^80 Bytes (1YiB) with the limit on a given
    > file being 2^55 bytes (32 PiB).

    Those sound correct, as UFS2 uses 64bit frag addresses, which when
    combined with a frag size of 16 (for 65536 bytes per frag) gives you
    2^80 for total file system size....

    as for the file size, The approximate max can be calculated by
    (blocksize / sizeof(ufs2_daddr_t)) ^ 3 * blocksize
    the real max would add in addition:
    (blocksize / sizeof(ufs2_daddr_t)) ^ 2 * blocksize +
    (blocksize / sizeof(ufs2_daddr_t)) * blocksize +
    9 * blocksize

    so, with a blocksize of 65536, and ufs2_daddr_t's size being 8 bytes,
    you end up with:
    (2^16 / 2^3) ^ 3 * 2^16
    (2^13)^3 * 2^16
    2^(13*3) * 2^16
    2^39 * 2^16
    2^(39 + 16)
    2^55

    but if you add the additional blocks, you'll end up with larger, but
    not enough to go to 2^56 for file sizes...

    > Are these numbers correct? I somehow remember the limits as
    > being much lower (of the order of 16TB or so).

    You might be thinking of UFS1... Now there is a funny thing that
    I found out about UFS2 and UFS1... UFS1 supports larger file
    sizes (not file system sizes) due to the fact that the ufs_daddr_t
    is smaller (32bits), means it can get more out of the indirect blocks
    than UFS2 can... UFS1 can have files of 2^58 compared to UFS2's 2^55... 

    -- 
  John-Mark Gurney				Voice: +1 415 225 5579
     "All that I will do, has been done, All that I have, has not."
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