From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9]) by lore.proxmox.com (Postfix) with ESMTPS id D8E581FF13F for ; Thu, 26 Feb 2026 09:46:20 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 96F01190BE; Thu, 26 Feb 2026 09:47:17 +0100 (CET) From: Maximiliano Sandoval To: pve-devel@lists.proxmox.com Subject: [PATCH docs v2 1/2] local-zfs: rephrase ARC limit Date: Thu, 26 Feb 2026 09:46:35 +0100 Message-ID: <20260226084639.107816-2-m.sandoval@proxmox.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260226084639.107816-1-m.sandoval@proxmox.com> References: <20260226084639.107816-1-m.sandoval@proxmox.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1772095582127 X-SPAM-LEVEL: Spam detection results: 0 AWL -0.973 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment RCVD_IN_VALIDITY_CERTIFIED_BLOCKED 0.618 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_RPBL_BLOCKED 0.734 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_SAFE_BLOCKED 0.78 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Message-ID-Hash: OKMQ5C6F4OQTXE7TPU23FPIV3DFXAOHC X-Message-ID-Hash: OKMQ5C6F4OQTXE7TPU23FPIV3DFXAOHC X-MailFrom: m.sandoval@proxmox.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: We rephrase the current section putting more emphasis on the current state of things given than Proxmox VE 8.1 was released over two years ago. We also document ZFS' default size. See [zfs-6a629f3] for more details. This also frames the problem for pre-existing setups in its own paragraph. [zfs-6a629f3] https://github.com/openzfs/zfs/commit/6a629f32344468ae81b264055916641480cb438d Signed-off-by: Maximiliano Sandoval --- local-zfs.adoc | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/local-zfs.adoc b/local-zfs.adoc index 85fa092..b3a462d 100644 --- a/local-zfs.adoc +++ b/local-zfs.adoc @@ -586,10 +586,15 @@ configured for the root user. Limit ZFS Memory Usage ~~~~~~~~~~~~~~~~~~~~~~ -ZFS uses '50 %' of the host memory for the **A**daptive **R**eplacement -**C**ache (ARC) by default. For new installations starting with {pve} 8.1, the -ARC usage limit will be set to '10 %' of the installed physical memory, clamped -to a maximum of +16 GiB+. This value is written to `/etc/modprobe.d/zfs.conf`. +ZFS uses '10 %' of the host memory, clamped to a maximum of +16 GiB+, for the +**A**daptive **R**eplacement **C**ache (ARC) by default. This value is written +to `/etc/modprobe.d/zfs.conf` during installation. + +Before {pve} 8.1, the ARC usage limit was not set during installation and +matched ZFS' default value which was either 62.5% starting on ZFS 2.3.0 or 50% +for older versions. For existing installations that predate {pve} 8.1, manual +steps would have to be performed in order to lower the usage limit as described +below. Allocating enough memory for the ARC is crucial for IO performance, so reduce it with caution. As a general rule of thumb, allocate at least +2 GiB Base + 1 -- 2.47.3