[lustre-discuss] [EXTERNAL] ZFS and OST Space Difference

Mohr, Rick mohrrf at ornl.gov
Tue Apr 6 13:34:04 PDT 2021


The drive sizes are 7.6 TB which translates to about 6.9 TiB (which is the unit that zpool uses for "T").  So the zpool sizes as just 10 x 6.9T = 69T since zpool shows the total amount of disk space available to the pool.  The usable space (which is what df is reporting) should be more like 0.8 x 69T = 55T.  I am not sure about the discrepancy of 3T.  Maybe that is due to some ZFS and/or Lustre overhead?


On 4/6/21, 3:49 PM, "lustre-discuss on behalf of Makia Minich" <lustre-discuss-bounces at lists.lustre.org on behalf of makia at systemfabricworks.com> wrote:

    I believe this was discussed a while ago, but I was unable to find clear answers, so I’ll re-ask in hopefully a slightly different way.
    On an OST, I have 30 drives, each at 7.6TB. I create 3 raidz2 zpools of 10 devices (ashift=12):

    [root at lustre47b ~]# zpool list
    oss55-0  69.9T  37.3M  69.9T        -         -     0%     0%  1.00x    ONLINE  -
    oss55-1  69.9T  37.3M  69.9T        -         -     0%     0%  1.00x    ONLINE  -
    oss55-2  69.9T  37.4M  69.9T        -         -     0%     0%  1.00x    ONLINE  -
    [root at lustre47b ~]#

    Running a mkfs.lustre against these (and the lustre mount) and I see:

    [root at lustre47b ~]# df -h | grep ost
    oss55-0/ost165             52T   27M   52T   1% /lustre/ost165
    oss55-1/ost166             52T   27M   52T   1% /lustre/ost166
    oss55-2/ost167             52T   27M   52T   1% /lustre/ost167
    [root at lustre47b ~]#

    Basically, we’re seeing a pretty dramatic loss in capacity (156TB vs 209.7TB, so a loss of about 50TB). Is there any insight on where this capacity is disappearing to? If there some mkfs.lustre or zpool option I missed in creating this? Is something just reporting slightly off and that space really is there?



    Makia Minich

    Chief Architect

    System Fabric Works
    "Fabric Computing that Works”

    "Oh, I don't know. I think everything is just as it should be, y'know?”
    - Frank Fairfield

More information about the lustre-discuss mailing list