ZFS Commands - Revision history

Wikisailor: /* Removing the L2ARC */

2026-02-15T01:48:15Z

Removing the L2ARC

@@ Line 115: / Line 115: @@
 The output shows the members of pearpool including the Lexar SSD. Now we can run the following command to remove the SSD from pearpool
   zpool remove pearpool ata-Lexar_SSD_NQ100_960GB_QCT180R0006120S334
 ===Managing Snapshots (The "Time Machine")===

Wikisailor: /* The L2ARC Index Requirement */

2026-02-15T00:45:48Z

The L2ARC Index Requirement

← Older revision		Revision as of 00:45, 15 February 2026
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	'''Update. After reviewing the usage of the of the cache we will now remove it as it is not doing any good and it is using some of the RAM so therefore in this case it is counter productive.		'''Update. After reviewing the usage of the of the cache we will now remove it as it is not doing any good and it is using some of the RAM so therefore in this case it is counter productive.


			====Removing the L2ARC====
			Having decided to remove the L2ARC we need to identify the SSD using the command:
			zpool status pearpool
			The output shows the members of pearpool including the Lexar SSD. Now we can run the following command to remove the SSD from pearpool
			zpool remove pearpool ata-Lexar_SSD_NQ100_960GB_QCT180R0006120S334

	===Managing Snapshots (The "Time Machine")===		===Managing Snapshots (The "Time Machine")===

Wikisailor: /* ARC: Understanding the RAM usage */

2026-02-15T00:25:21Z

ARC: Understanding the RAM usage

← Older revision		Revision as of 00:25, 15 February 2026
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	To see what the current value is (the one the kernel is actually using right now), we can cat that same location:		To see what the current value is (the one the kernel is actually using right now), we can cat that same location:
	cat /sys/module/zfs/parameters/zfs_arc_max		cat /sys/module/zfs/parameters/zfs_arc_max


	====The "Ephemeral" Nature====		====The "Ephemeral" Nature====
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	update-initramfs -u		update-initramfs -u
	This ensures ZFS loads with this limit the moment the server turns on.		This ensures ZFS loads with this limit the moment the server turns on.


			====The L2ARC Index Requirement====

			Adding a L2ARC does provide a high speed cache to an array of ZFS HDDs and may boost read performance but it does not come for free because the cache has to be indexed in RAM so that the system can check the contents of the cache before it searches the HDDs. On a standard setup, every 8KB block on the SSD requires roughly 70 to 80 bytes of system RAM for the index. We have a 1 TB SSD that is acting as a L2ARC. 1TB is roughly 1,000,000,000,000 bytes and if that was filled with 8KB blocks, it would have ~125 million entries. 125,000,000 times 80 bytes is approximately 10GB of RAM. In our system we would need more than the 10GB of RAM assigned to the cache to contain the index, any less will make the cache useless because the index will be constantly paged in and out of memory. Due to the high cost of the cache it is important to check how much use it is in real life. The command arcstatcan be used to show what the size of the cache is in use and it's hits run the following
			arcstat -f l2size,l2hits,l2read

			'''Update. After reviewing the usage of the of the cache we will now remove it as it is not doing any good and it is using some of the RAM so therefore in this case it is counter productive.

	===Managing Snapshots (The "Time Machine")===		===Managing Snapshots (The "Time Machine")===

Wikisailor: /* The "Ephemeral" Nature */

2026-02-14T23:18:13Z

The "Ephemeral" Nature

← Older revision		Revision as of 23:18, 14 February 2026
Line 91:		Line 91:

	====The "Ephemeral" Nature====		====The "Ephemeral" Nature====
	Because zfs_arc_max exists in the /sys/ directory (which is a temporary RAM-based filesystem), ~~this~~ change will be lost when Pear reboots. To make it permanent, we have to move the setting from the virtual /sys/ folder to a real configuration file on the disk:		Because zfs_arc_max exists in the /sys/ directory (which is a temporary RAM-based filesystem), the above change will be lost when Pear reboots. To make it permanent, we have to move the setting from the virtual /sys/ folder to a real configuration file on the disk:
	* Create the file:		* Create the file:
	nano /etc/modprobe.d/zfs.conf		nano /etc/modprobe.d/zfs.conf

Wikisailor: /* ARC: Understanding the RAM usage */

2026-02-14T23:14:25Z

ARC: Understanding the RAM usage

← Older revision		Revision as of 23:14, 14 February 2026
Line 85:		Line 85:
	ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command		ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command
	arcstat		arcstat
	If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb '''NB'''we don't technically need to be on the 1024 byte boundaries but as the OS will generally use RAM in pages it will make more sense to stick to 1024x1024x1024 x ''gigabytes''		If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb '''NB''' we don't technically need to be on the 1024 byte boundaries but as the OS will generally use RAM in pages it will make more sense to stick to 1024x1024x1024 x ''gigabytes''
	echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max		echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max
	To see what the current value is (the one the kernel is actually using right now), we can cat that same location:		To see what the current value is (the one the kernel is actually using right now), we can cat that same location:

Wikisailor: /* ARC: Understanding the RAM usage */

2026-02-14T23:13:43Z

ARC: Understanding the RAM usage

← Older revision		Revision as of 23:13, 14 February 2026
Line 85:		Line 85:
	ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command		ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command
	arcstat		arcstat
	If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb '''NB'''we don't technically need to be on the 1024 byte boundaries but as the OS will generally use RAM in pages it will make more sense to stick to ~~1024x1024x1024x~~''gigabytes''		If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb '''NB'''we don't technically need to be on the 1024 byte boundaries but as the OS will generally use RAM in pages it will make more sense to stick to 1024x1024x1024 x ''gigabytes''
	echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max		echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max
	To see what the current value is (the one the kernel is actually using right now), we can cat that same location:		To see what the current value is (the one the kernel is actually using right now), we can cat that same location:

Wikisailor: /* ARC: Understanding the RAM usage */

2026-02-14T23:13:22Z

ARC: Understanding the RAM usage

← Older revision		Revision as of 23:13, 14 February 2026
Line 85:		Line 85:
	ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command		ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command
	arcstat		arcstat
	If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb		If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb '''NB'''we don't technically need to be on the 1024 byte boundaries but as the OS will generally use RAM in pages it will make more sense to stick to 1024x1024x1024x''gigabytes''
	echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max		echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max
	To see what the current value is (the one the kernel is actually using right now), we can cat that same location:		To see what the current value is (the one the kernel is actually using right now), we can cat that same location:

Wikisailor: /* ARC: Understanding the RAM usage */

2026-02-14T23:04:55Z

ARC: Understanding the RAM usage

← Older revision		Revision as of 23:04, 14 February 2026
Line 86:		Line 86:
	arcstat		arcstat
	If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb		If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb
	echo 8589934592 > /sys/module/zfs/parameters/~~zfs_arc_maxsee what th~~		echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max
	To see what the current value is (the one the kernel is actually using right now), we can cat that same location:		To see what the current value is (the one the kernel is actually using right now), we can cat that same location:
	cat /sys/module/zfs/parameters/zfs_arc_max		cat /sys/module/zfs/parameters/zfs_arc_max

			====The "Ephemeral" Nature====
			Because zfs_arc_max exists in the /sys/ directory (which is a temporary RAM-based filesystem), this change will be lost when Pear reboots. To make it permanent, we have to move the setting from the virtual /sys/ folder to a real configuration file on the disk:
			* Create the file:
			nano /etc/modprobe.d/zfs.conf
			* Write the option:
			options zfs zfs_arc_max=8589934592
			* Commit it to RAMFS at next boot:
			update-initramfs -u
			This ensures ZFS loads with this limit the moment the server turns on.

	===Managing Snapshots (The "Time Machine")===		===Managing Snapshots (The "Time Machine")===

Wikisailor: /* ARC: Understanding the RAM usage */

2026-02-14T22:59:09Z

ARC: Understanding the RAM usage

← Older revision		Revision as of 22:59, 14 February 2026
Line 85:		Line 85:
	ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command		ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command
	arcstat		arcstat
	If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x ~~times~~ 1024^3		If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x 1024^3 for 8gb
	echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max		echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_maxsee what th
			To see what the current value is (the one the kernel is actually using right now), we can cat that same location:
			cat /sys/module/zfs/parameters/zfs_arc_max

	===Managing Snapshots (The "Time Machine")===		===Managing Snapshots (The "Time Machine")===

Wikisailor: /* ARC: Understanding the RAM usage */

2026-02-14T22:55:47Z

ARC: Understanding the RAM usage

← Older revision		Revision as of 22:55, 14 February 2026
Line 85:		Line 85:
	ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command		ZFS uses the Adaptive Replacement Cache (ARC). It will attempt to use as much free RAM as possible to cache your most frequent data. The misconception is that we may see Proxmox reporting 95% RAM usage. This is usually ZFS being efficient, not a "memory leak." The Handshake: If a VM or LXC container needs that RAM, ZFS will release it instantly. We can check your cache efficiency with the command
	arcstat		arcstat
			If we find the ARC (Adaptive Replacement Cache) is consuming more RAM than we would like even though it’s designed to give it back when needed we can place a "hard cap" on it. On a Proxmox host like Pear, this is done by modifying the ZFS module parameters. We don't "remove" it (as ZFS needs a cache to function), but we can strictly limit its growth. To directly write a value to the Kernel Module Parameter in real time, we echo the number of bytes directly to it eg 8 x times 1024^3
			echo 8589934592 > /sys/module/zfs/parameters/zfs_arc_max

	===Managing Snapshots (The "Time Machine")===		===Managing Snapshots (The "Time Machine")===