Re: ZFS on root with dedupe

Reply: Andrea Venturoli : "Re: ZFS on root with dedupe"
In reply to: Robert Fitzpatrick : "ZFS on root with dedupe"
Go to: [ bottom of page ] [ top of archives ] [ this month ]

From: Paul Mather <paul_at_gromit.dlib.vt.edu>
Date: Sat, 22 Apr 2023 15:46:13 UTC

On Apr 22, 2023, at 11:25 AM, Robert Fitzpatrick <robert@webtent.org> wrote:


> Hi,
> 
> I installed FreeBSD 13.1 server with ZFS raid 10 to serve a PostgreSQL database, LDAP and DNS. I never noticed until today, I installed some more memory and was checking status after the starting up. DEDUP appears enabled, is that by default? I certainly did not enable. Does this mean it is in fact enabled and what are the repercussions of disabling now?
> 
>> root@db1:~ # zpool list
>> NAME   SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
>> zdb1   262G  26.1G   236G        -         -     7%     9%  1.00x    ONLINE  -
>> root@db1:~ # zpool status
>>  pool: zdb1
>> state: ONLINE
>>  scan: scrub repaired 0B in 00:04:52 with 0 errors on Thu Apr 13 10:46:22 2023
>> config:
>>        NAME        STATE     READ WRITE CKSUM
>>        zdb1        ONLINE       0     0     0
>>          mirror-0  ONLINE       0     0     0
>>            ada0p3  ONLINE       0     0     0
>>            ada1p3  ONLINE       0     0     0
>>          mirror-1  ONLINE       0     0     0
>>            ada2p3  ONLINE       0     0     0
>>            ada3p3  ONLINE       0     0     0
>> root@db1:~ # zfs list
>> NAME                USED  AVAIL     REFER  MOUNTPOINT
>> zdb1               26.0G   228G       96K  /zdb1
>> zdb1/ROOT          24.8G   228G       96K  none
>> zdb1/ROOT/default  24.8G   228G     14.6G  /
>> zdb1/tmp           1.12M   228G      200K  /tmp
>> zdb1/usr           1.17G   228G       96K  /usr
>> zdb1/usr/home      1.31M   228G     1.30M  /usr/home
>> zdb1/usr/ports     1.17G   228G     1.17G  /usr/ports
>> zdb1/usr/src         96K   228G       96K  /usr/src
>> zdb1/var           5.35M   228G       96K  /var
>> zdb1/var/audit       96K   228G       96K  /var/audit
>> zdb1/var/crash       96K   228G       96K  /var/crash
>> zdb1/var/log       4.78M   228G      660K  /var/log
>> zdb1/var/mail       200K   228G      144K  /var/mail
>> zdb1/var/tmp


Just because there is a DEDUP column in the "zpool list" output does not mean deduplication is enabled.  Deduplication is a per-fileset option, so a better way of determining whether it is enabled for any of your ZFS filesets is to execute the following command:

	zfs get dedup

That will show you the "dedup" property for all of your filesets.  In my case, all the non-snapshot filesets show "dedup" as being "off" even though I get "DEDUP" shown as "1.00x" in the "zpool list" output.  (Which still makes sense: 1.00x deduplication is consistent with deduplication being off.)

Cheers,

Paul.