From: Gionatan Danti <g.danti@assyoma.it>
To: Demi Marie Obenour <demi@invisiblethingslab.com>
Cc: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] Why is the performance of my lvmthin snapshot so poor
Date: Thu, 16 Jun 2022 15:22:09 +0200 [thread overview]
Message-ID: <7caac0c00c5c7cd93fdf50b62e2e7907@assyoma.it> (raw)
In-Reply-To: <Yqrhmwwbp5KfiEWb@itl-email>
Il 2022-06-16 09:53 Demi Marie Obenour ha scritto:
> That seems reasonable. My conclusion is that dm-thin (which is what
> LVM
> uses) is not a good fit for workloads with a lot of small random writes
> and frequent snapshots, due to the 64k minimum chunk size. This also
> explains why dm-thin does not allow smaller blocks: not only would it
> only support very small thin pools, it would also have massive metadata
> write overhead. Hopefully dm-thin v2 will improve the situation.
I think that, in this case, no free lunch really exists. I tried the
following thin provisioning methods, each with its strong & weak points:
lvmthin: probably the more flexible of the mainline kernel options. You
pay for r/m/w only when allocating a small block (say 4K) the first time
after taking a snapshot. It is fast and well integrated with lvm command
line. Con: bad behavior on out-of-space condition
xfs + reflink: a great, simple to use tool when applicable. It has a
very small granularity (4K) with no r/m/w. Cons: requires fine tuning
for good performance when reflinking big files; IO freezes during
metadata copy for reflink; a very small granularity means sequential IO
is going to suffer heavily (see here for more details:
https://marc.info/?l=linux-xfs&m=157891132109888&w=2)
btrfs: very small granularity (4K) and many integrated features. Cons:
bad performance overall, especially when using mechanical HDD
vdo: is provides small granularity (4K) thin provisioning, compression
and deduplication. Cons: (still) out-of-tree; requires a powerloss
protected writeback cache to maintain good performance; no snapshot
capability
zfs: designed for the ground up for pervasive CoW, with many features
and ARC/L2ARC. Cons: out-of-tree; using small granularity (4K) means bad
overall performance; using big granularity (128K by default) is a
necessary compromise for most HDD pools.
For what it is worth, I settled on ZFS when using out-of-tree modules is
not an issue and lvmthin otherwise (but I plan to use xfs + reflink more
in the future).
Do you have any information to share about dm-thin v2? I heard about it
some years ago, but I found no recent info.
Regards.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
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next prev parent reply other threads:[~2022-06-16 13:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-13 8:49 [linux-lvm] Why is the performance of my lvmthin snapshot so poor Zhiyong Ye
2022-06-14 7:04 ` Gionatan Danti
2022-06-14 10:16 ` Zhiyong Ye
2022-06-14 12:56 ` Gionatan Danti
2022-06-14 13:29 ` Zhiyong Ye
2022-06-14 14:54 ` Gionatan Danti
2022-06-15 7:42 ` Zhiyong Ye
2022-06-15 9:34 ` Gionatan Danti
2022-06-15 9:46 ` Zhiyong Ye
2022-06-15 12:40 ` Gionatan Danti
2022-06-15 16:39 ` Demi Marie Obenour
2022-06-16 7:53 ` Demi Marie Obenour
2022-06-16 13:22 ` Gionatan Danti [this message]
2022-06-16 16:19 ` Demi Marie Obenour
2022-06-16 19:50 ` Gionatan Danti
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