[lustre-discuss] ZFS and OST Space Difference

Saravanaraj Ayyampalayam ansraj at gmail.com
Tue Apr 6 14:19:16 PDT 2021


I think you are correct. ‘zpool list’ shows raw space, ‘zfs list’ shows the space after reservation for parity, etc.. In a 10 disk raidz2 ~24% of the space is reserved for parity.
This website helps in calculating ZFS capacity. https://wintelguy.com/zfs-calc.pl <https://wintelguy.com/zfs-calc.pl>

-Raj

> On Apr 6, 2021, at 4:56 PM, Laura Hild via lustre-discuss <lustre-discuss at lists.lustre.org> wrote:
> 
> > I am not sure about the discrepancy of 3T.  Maybe that is due to some ZFS and/or Lustre overhead?
> 
> Slop space?
> 
>    https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html#spa-slop-shift <https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html#spa-slop-shift>
> 
> -Laura
> 
> 
> Od: lustre-discuss <lustre-discuss-bounces at lists.lustre.org <mailto:lustre-discuss-bounces at lists.lustre.org>> v imenu Mohr, Rick via lustre-discuss <lustre-discuss at lists.lustre.org <mailto:lustre-discuss at lists.lustre.org>>
> Poslano: torek, 06. april 2021 16:34
> Za: Makia Minich <makia at systemfabricworks.com <mailto:makia at systemfabricworks.com>>; lustre-discuss at lists.lustre.org <mailto:lustre-discuss at lists.lustre.org> <lustre-discuss at lists.lustre.org <mailto:lustre-discuss at lists.lustre.org>>
> Zadeva: Re: [lustre-discuss] [EXTERNAL] ZFS and OST Space Difference
>  
> Makia,
> 
> 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?
> 
> --Rick
> 
> 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
>     NAME            SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
>     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?
> 
>     Thanks.
> 
>> 
> 
>     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
> 
> 
> 
> 
> 
> 
> 
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