This article explains the minor alarm "SSD at slot [X] (/dev/sdb) encountered errors" on the device and ways to mitigate the same.

root@SRX> show chassis alarms no-forwarding

1 alarms currently active
Alarm time              Class Description
2023-11-09 10:02:02 UTC Minor SSD at slot 1 (/dev/sdb) encountered errrors.



root@SRX> show chassis hardware detail no-forwarding

Hardware inventory:
Item            Version Part number Serial number    Description

Chassis                               AAAABBBBBCCCC    SRX4600
Midplane        REV 59  750-069375  AAAAXXXX       SRX4600 Midplane

Routing Engine 0         BUILTIN     BUILTIN          SRX Routing Engine

Pseudo CB 0
 Mezz          REV 16  711-066896  AAAAXXXX        Control Mezz Board

Logs:

Nov 9 10:02:02 LCC: [Alarm SET] Object 143 reason 120 Device FRU FPC 0, reason SSD Monitoring Erro(SSD at slot 1 (/dev/sdb) encountered errrors.), color 2, slot 0 Alarm id 2399142008

Nov 9 10:02:02 LCC: send: yellow alarm set, device FRU FPC 0, reason SSD at slot 1 (/dev/sdb) encountered errrors.

In SRX4600, the routing engine is built in with SSD attached to it.

To resolve the issue kindly try reseating (unplug/plug) the SSD into the SRX in a safe MW and check if that clears the error.
Alarms will clear eventually in sometime after the maintenance is complete.

Note:You need to power off the SRX to reseat/replace a SSD from the firewall.

Field-Replaceable Units in an SRX4600 Services Gateway

https://www.juniper.net/documentation/en_US/release-independent/junos/topics/concept/services-gateway-srx4600-frus.html

Replacing an SRX4600 Services Gateway SSD

https://www.juniper.net/documentation/en_US/release-independent/junos/topics/task/installation/services-gateway-srx4600-ssd-replacing.html