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To: petefrench@ingresso.co.uk, se@freebsd.org
Subject: Re: Does FreeBSD 13 disable the VEV cache in ZFS ?
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From: Pete French <petefrench@ingresso.co.uk>
Date: Fri, 14 May 2021 13:34:52 +0100
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> Could you check the values of the following sysctl variables:
>
> vfs.zfs.vdev.cache_size
> vfs.zfs.vdev.cache_bshift
> vfs.zfs.vdev.cache_max
> kstat.zfs.misc.vdev_cache_stats.misses
> kstat.zfs.misc.vdev_cache_stats.hits
> kstat.zfs.misc.vdev_cache_stats.delegations

As predicted, all zero, apart from bshift which is 16 and max which is 16384


> https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html#zfs-vdev-cache-size
>
> Quote:
>
> Note: with the current ZFS code, the vdev cache is not helpful and in some
> cases actually harmful. Thus it is disabled by setting the zfs_vdev_cache_size = 0

Ah, thats the thing I should have found msyelf I guess! :-) Actually, if smarter
people than me think that its not useful on OpenZFS, then I shall probably
leave it disabled. Generally people have a good reason for doing things.

I shall have a read,and thankyou for confirming this (and thankyou for
maintinaing zfs-stats! which is an invalauble tool I have found over the years)


-pete.