[pve-devel] [PATCH storage] iscsi: disable Open-iSCSI login retries to avoid blocking pvestatd

[pve-devel] [PATCH storage] iscsi: disable Open-iSCSI login retries to avoid blocking pvestatd

[Friedrich Weber]

Since 90c1b10 ("fix #254: iscsi: add support for multipath targets"),
iSCSI storage activation checks whether a session exists for each
discovered portal. If there is a discovered portal without a session,
it performs a discovery and login in the hope of establishing a
session to the portal. If the portal is unreachable when trying to log
in, Open-iSCSI's default behavior is to retry for up to 2 minutes, as
explained in /etc/iscsi/iscid.conf:

> # The default node.session.initial_login_retry_max is 8 and
> # node.conn[0].timeo.login_timeout is 15 so we have:
> #
> # node.conn[0].timeo.login_timeout * \
> node.session.initial_login_retry_max = 120s

If pvestatd is activating the storage, it will be blocked during that
time, which is undesirable. This is particularly unfortunate if the
target announces portals that the host permanently cannot reach. In
that case, every pvestatd iteration will take 2 minutes. While it can
be argued that such setups are misconfigured, it is still desirable to
keep the fallout of that misconfiguration as low as possible.

In order to reduce the time Open-iSCSI tries to log in, instruct
Open-ISCSI to not perform login retries for that target. For this, set
node.session.initial_login_retry_max for the target to 0. This setting
is stored in Open-iSCSI's records under /etc/iscsi/nodes. As these
records are overwritten with the defaults from /etc/iscsi/iscsid.conf
on discovery, the setting needs to be applied after discovery.

With this setting, one login attempt should take at most 15 seconds.
This is still higher than pvestatd's iteration time of 10 seconds, but
more tolerable. Logins will still be continuously retried by pvestatd
in every iteration until there is a session to each discovered portal.

Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
---
 src/PVE/Storage/ISCSIPlugin.pm | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/PVE/Storage/ISCSIPlugin.pm b/src/PVE/Storage/ISCSIPlugin.pm
index 2bdd9a2..efd9de4 100644
--- a/src/PVE/Storage/ISCSIPlugin.pm
+++ b/src/PVE/Storage/ISCSIPlugin.pm
@@ -132,6 +132,14 @@ sub iscsi_login {
     eval { iscsi_discovery($portals); };
     warn $@ if $@;
 
+    # Disable retries to avoid blocking pvestatd for too long, next iteration will retry anyway
+    eval {
+	my $cmd = [$ISCSIADM, '--mode', 'node', '--targetname', $target, '--op', 'update',
+	    '--name', 'node.session.initial_login_retry_max', '--value', '0'];
+	run_command($cmd);
+    };
+    warn $@ if $@;
+
     run_command([$ISCSIADM, '--mode', 'node', '--targetname',  $target, '--login']);
 }
 
-- 
2.39.5



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Re: [pve-devel] [PATCH storage] iscsi: disable Open-iSCSI login retries to avoid blocking pvestatd

[Mira Limbeck]

On 10/11/24 11:37, Friedrich Weber wrote:
> Since 90c1b10 ("fix #254: iscsi: add support for multipath targets"),
> iSCSI storage activation checks whether a session exists for each
> discovered portal. If there is a discovered portal without a session,
> it performs a discovery and login in the hope of establishing a
> session to the portal. If the portal is unreachable when trying to log
> in, Open-iSCSI's default behavior is to retry for up to 2 minutes, as
> explained in /etc/iscsi/iscid.conf:
> 
>> # The default node.session.initial_login_retry_max is 8 and
>> # node.conn[0].timeo.login_timeout is 15 so we have:
>> #
>> # node.conn[0].timeo.login_timeout * \
>> node.session.initial_login_retry_max = 120s
> 
> If pvestatd is activating the storage, it will be blocked during that
> time, which is undesirable. This is particularly unfortunate if the
> target announces portals that the host permanently cannot reach. In
> that case, every pvestatd iteration will take 2 minutes. While it can
> be argued that such setups are misconfigured, it is still desirable to
> keep the fallout of that misconfiguration as low as possible.
> 
> In order to reduce the time Open-iSCSI tries to log in, instruct
> Open-ISCSI to not perform login retries for that target. For this, set
> node.session.initial_login_retry_max for the target to 0. This setting
> is stored in Open-iSCSI's records under /etc/iscsi/nodes. As these
> records are overwritten with the defaults from /etc/iscsi/iscsid.conf
> on discovery, the setting needs to be applied after discovery.
> 
> With this setting, one login attempt should take at most 15 seconds.
> This is still higher than pvestatd's iteration time of 10 seconds, but
> more tolerable. Logins will still be continuously retried by pvestatd
> in every iteration until there is a session to each discovered portal.
> 
> Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
> ---
>  src/PVE/Storage/ISCSIPlugin.pm | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/src/PVE/Storage/ISCSIPlugin.pm b/src/PVE/Storage/ISCSIPlugin.pm
> index 2bdd9a2..efd9de4 100644
> --- a/src/PVE/Storage/ISCSIPlugin.pm
> +++ b/src/PVE/Storage/ISCSIPlugin.pm
> @@ -132,6 +132,14 @@ sub iscsi_login {
>      eval { iscsi_discovery($portals); };
>      warn $@ if $@;
>  
> +    # Disable retries to avoid blocking pvestatd for too long, next iteration will retry anyway
> +    eval {
> +	my $cmd = [$ISCSIADM, '--mode', 'node', '--targetname', $target, '--op', 'update',
> +	    '--name', 'node.session.initial_login_retry_max', '--value', '0'];
As shortly discussed off-list, this should probably follow a similar
style as the `Wrapping Arguments` section in the Perl Style Guide, but
grouping option and value together in the same line?
https://pve.proxmox.com/wiki/Perl_Style_Guide#Wrapping_Arguments

> +	run_command($cmd);
> +    };
> +    warn $@ if $@;
> +
>      run_command([$ISCSIADM, '--mode', 'node', '--targetname',  $target, '--login']);
>  }
>  

Tested this with 4 portals by disconnecting 2. With this patch the
pvestatd update time was at ~30 seconds, matching 2 failed logins.
Without the patch it was ~484 seconds.

Since a login fails in 7 seconds, the old behavior actually did more
than 8 retries, see the comment for `initial_login_retry_max`:
# Note that if the login fails
# quickly (before node.conn[0].timeo.login_timeout fires) because the
network
# layer or the target returns an error, iscsid may retry the login more than
# node.session.initial_login_retry_max times.

So especially for the cases of `no route to host` this should improve
the update time significantly for multiple portals where some are never
reachable.


Consider this patch:
Tested-by: Mira Limbeck <m.limbeck@proxmox.com>
Reviewed-by: Mira Limbeck <m.limbeck@proxmox.com>


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Re: [pve-devel] [PATCH storage] iscsi: disable Open-iSCSI login retries to avoid blocking pvestatd

[Friedrich Weber]

Thanks for the test and review!

On 11/10/2024 13:20, Mira Limbeck wrote:
> [...]
>> --- a/src/PVE/Storage/ISCSIPlugin.pm
>> +++ b/src/PVE/Storage/ISCSIPlugin.pm
>> @@ -132,6 +132,14 @@ sub iscsi_login {
>>      eval { iscsi_discovery($portals); };
>>      warn $@ if $@;
>>  
>> +    # Disable retries to avoid blocking pvestatd for too long, next iteration will retry anyway
>> +    eval {
>> +	my $cmd = [$ISCSIADM, '--mode', 'node', '--targetname', $target, '--op', 'update',
>> +	    '--name', 'node.session.initial_login_retry_max', '--value', '0'];
> As shortly discussed off-list, this should probably follow a similar
> style as the `Wrapping Arguments` section in the Perl Style Guide, but
> grouping option and value together in the same line?
> https://pve.proxmox.com/wiki/Perl_Style_Guide#Wrapping_Arguments

Good point. I sent a v2 addressing this (and also rewording the commit
message, because I realized the v1 one was not really correct):

https://lore.proxmox.com/pve-devel/20241011125821.58224-1-f.weber@proxmox.com/


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