---
# System prepended metadata

title: ZFS Research on Alice

---

# ZFS Research on Alice

### State of Alice after Shutting down

``` 
/dev/sdg ata-JAJS600M2TB_AA202100000031004406
/dev/sdh ata-JAJS600M2TB_AA202100000031004409
```

```
[root@alice]: /dev/disk># zpool status
  pool: data
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
        The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(7) for details.
  scan: resilvered 2.48G in 02:09:28 with 0 errors on Tue Nov 29 21:32:38 2022
config:

        NAME                                      STATE     READ WRITE CKSUM
        data                                      ONLINE       0     0     0
          ata-CT1000MX500SSD1_1937E21EA7CD        ONLINE       0     0     0
          mirror-1                                ONLINE       0     0     0
            ata-CT1000MX500SSD1_1914E1F7B15F      ONLINE       0     0     0
            sdf                                   ONLINE       0     0     0
          mirror-2                                ONLINE       0     0     0
            ata-JAJS600M2TB_AA202100000031004406  ONLINE       0     0     0
            ata-JAJS600M2TB_AA202100000031004409  ONLINE       0     0     0
          ata-CT1000MX500SSD1_1914E1F7DAA6        ONLINE       0     0     0

errors: No known data errors
```

It looks like `/dev/sdg` and `/dev/sdh` (the problematic disks) are in `mirror-2`.

### Hypothesis 

We believe that `zfs` is responsible for the high iowait and io utilization on NFS

### Observation

Removing ZFS snapshots on Alice caused a spike in IO utilization

```bash
zfs list -t snapshot
zfs list -t all

zfs list -H -o name -t snapshot | xargs -n1 zfs destroy
```

![](https://i.imgur.com/pIsbs8x.png)

### Removing ZFS snapshots 

![](https://i.imgur.com/RcTRWoW.png)
