ZFS

Links

• http://open-zfs.org
• http://www.edplese.com/samba-with-zfs.html
• ZFS calculator
• ZFS clustering
• https://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/ ZFS and ECC]
• ZFS troubleshooting/disk replacement
• Creating a ZFS HA Cluster using shared or shared-nothing storage
• ZFS 101
• Raidz expansion
• Basic guide to working with zfs

Documentation

• zfs manpage
• ZFS on Linux
• openzfs wiki
• https://wiki.gentoo.org/wiki/ZFS
• ZFS cheatsheet
• http://wiki.freebsd.org/ZFSQuickStartGuide
• Opensolaris ZFS intro
• raidz types reference

ARC/Caching

• Configuring ZFS Cache for High-Speed IO
• ZFS Arc various sizes
• Activity of the ZFS ARC
• Understanding ARC hits
• ZFS Caching

Tuning ZFS

• ZFS Performance and Tuning
• Using and tuning ARC

Commands

Getting arc statistics

arc_summary

Tip, for details use

arc_summary -d

There is also

cat /proc/spl/kstat/zfs/arcstats

Terms and acronyms

vdev

Virtual Device.

• ZFS Virtual disks

ARC

Adaptive Replacement Cache

Portion of RAM used to cache data to speed up read performance

L2ARC

Level 2 Adaptive Replacement Cache

"L2ARC is usually considered if hit rate for the ARC is below 90% while having 64+ GB of RAM"

SSD cache

DMU

Data Management Unit

MFU

Most Frequently Used

MRU

Most Recently Used

ZIL

the space synchronous writes are logged before the confirmation is sent back to the client

prefetch

• Tuning of the ZFS module
• Understanding ZFS prefetch

HOWTO

Create zfs filesystem

zfs create poolname/fsname

this also creates mountpoint

Add vdev to pool

zpool add mypool raidz1 sdg sdh sdi

Replace disk in zfs

Some links

• https://itectec.com/ubuntu/ubuntu-replacing-a-dead-disk-in-a-zpool/

Get information first:

Name of disk

zpool status

Find uid of disk to replace

take it offline

zpool offline poolname ata-WDC_WD20EFRX-68EUZN0_WD-WCC4M5RLZC6V

Get the disk guid:

zdb

guid: 15233236897831806877

Get list of disk by id:

ls -al /dev/disk/by-id

Save the id, shutdown, replace disk, boot:

Find the new disk:

ls -al /dev/disk/by-id

Run replace command. The id is the guid of the old disk, name is of the new disk

zpool replace tank /dev/disk/by-id/13450850036953119346 /dev/disk/by-id/ata-ST4000VN000-1H4168_Z302FQVZ

Showing information about ZFS pools and datasets

Show pools with sizes

zpool list 

or

zpool list -H -o name,size

Show reservations on datasets

zfs list -o name,reservations

Swap on zfs

https://askubuntu.com/questions/228149/zfs-partition-as-swap

vdevs

multiple vdevs

Multiple vdevs in a zpool get striped. What about balance?

invalid vdev specification

Probably means you need -f

Tuning arc settings

See Tuning ZFS modules parameters

zfs_arc_max

Linux defaults to giving 50% of RAM to arc, this is when:

cat /sys/module/zfs/parameters/zfs_arc_max
0
grep c_max /proc/spl/kstat/zfs/arcstats

To change this:

echo 5368709120 > /sys/module/zfs/parameters/zfs_arc_max

and add to /etc/modprobe.d/zfs.conf

zfs zfs_arc_max=5368709120

maybe you need

echo 3 > /proc/sys/vm/drop_caches

Tune zfs_arc_dnode_limit_percent

Assuming zfs_arc_dnode_limit = 0:

echo 20 > /sys/module/zfs/parameters/zfs_arc_dnode_limit_percent

In /etc/modprobe.d/zfs.conf:

options zfs zfs_arc_dnode_limit_percent=20

FAQ

show status and disks

zpool status

show drives/pools

zfs list
      

check raid level

zfs list -a

Estimate raidz speeds

raidz1: N/(N-1) * IOPS
raidz2: N/(N-2) * IOPS
raidz3: N/(N-3) * IOPS

VDEV cache disabled, skipping section

Looks like you just don't have l2arc cache