[zfs-discuss] ZFS eating up all 16 GB RAM when combining 4k blocksize ZVOL with XFS

Gordan Bobic gordan.bobic at gmail.com
Tue Nov 13 11:19:49 EST 2018

With XFS on zvol I would imagine you are double-caching everything. Have
you set primarycache=metadata on your zvols?

On Tue, Nov 13, 2018 at 3:22 PM Omar Siam via zfs-discuss <
zfs-discuss at list.zfsonlinux.org> wrote:

> Hi Paul!
> I would recommend using the 0.7.11 dkms versions of zfs and spl. Too many
> new features and setups in there.
> I'm sure the Ubuntu team backports any critical fix. Just the enterprise
> Linux thing of never raise the version number. But I agree with you there
> were some important fixes between 0.7.5 and 0.7.11.
> The ARC *will* take up at least half your RAM if you do not limit it in
> your grub.cfg moreso if youve got zraid setups going on.
> Well I want that to happen. In this setup the only thing that should use
> RAM are ZFS and XFS or SCST for iSCSI. But I am still puzzled that this
> setup can use more than double the configured ARC size in a matter of
> seconds.
> As for XFS - Im not sure whats happening there. Shouldnt be anything too
> crazy.
> On Mon, Nov 12, 2018, 18:07 Paul Gorman <pagorman at asu.edu wrote:
>> Add to the grub/rEfind boot args for the kernel:
>> zfs.zfs_arc_max=536870912 #(for 512MB cap zfs memory usage, expressed in
>> bytes)
>> Though you'll likely want 512MiB-1GiB per physical disk.
>> Yes with this low setting it works. I would really like to use more of
> the RAM as ARC.
> If possible the ZFS/SPL code should not just use all available free RAM
> and then some more out of the blue. Seems at least there has to be a
> different default value than half the RAM if there are reproducable cases
> where that just more than doubles. No user expects the filesystem code to
> just exhaust all memory. Swap changes nothing in this respect by the way.
> Best regards
> Omar
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