18.9. Detecting and replacing a broken NVDIMM device

1. Detect which NVDIMM device is failing
2. Back up data stored on it
3. Physically replace the device

Procedure

1. Detect the broken device:

   # ndctl list --dimms --regions --health
   {
     "dimms":[
       {
         "dev":"nmem1",
         "id":"8089-a2-1834-00001f13",
         "handle":17,
         "phys_id":32,
         "security":"disabled",
         "health":{
           "health_state":"ok",
           "temperature_celsius":35.0,
           [...]
         }
   [...]
   }

2. Find the phys_id attribute of the broken NVDIMM:

   # ndctl list --dimms --human

   From the previous example, you know that nmem0 is the broken NVDIMM. Therefore, find the phys_id attribute of nmem0.

   In the following example, the phys_id is 0x10:

   # ndctl list --dimms --human
   
   [
     {
       "dev":"nmem1",
       "id":"XXXX-XX-XXXX-XXXXXXXX",
       "handle":"0x120",
       "phys_id":"0x1c"
     },
     {
       "dev":"nmem0",
       "id":"XXXX-XX-XXXX-XXXXXXXX",
       "handle":"0x20",
       "phys_id":"0x10",
       "flag_failed_flush":true,
       "flag_smart_event":true
     }
   ]

3. Find the memory slot of the broken NVDIMM:

   # dmidecode

   In the output, find the entry where the Handle identifier matches the phys_id attribute of the broken NVDIMM. The Locator field lists the memory slot used by the broken NVDIMM.

   In the following example, the nmem0 device matches the 0x0010 identifier and uses the DIMM-XXX-YYYY memory slot:

   # dmidecode
   
   ...
   Handle 0x0010, DMI type 17, 40 bytes
   Memory Device
           Array Handle: 0x0004
           Error Information Handle: Not Provided
           Total Width: 72 bits
           Data Width: 64 bits
           Size: 125 GB
           Form Factor: DIMM
           Set: 1
           Locator: DIMM-XXX-YYYY
           Bank Locator: Bank0
           Type: Other
           Type Detail: Non-Volatile Registered (Buffered)
   ...

4. Back up all data in the namespaces on the NVDIMM. If you do not back up the data before replacing the NVDIMM, the data will be lost when you remove the NVDIMM from your system.

   주의

   In some cases, such as when the NVDIMM is completely broken, the backup might fail.

   To prevent this, regularly monitor your NVDIMM devices using S.M.A.R.T. as described in Monitoring NVDIMM health using S.M.A.R.T. and replace failing NVDIMMs before they break.

5. List the namespaces on the NVDIMM:

   # ndctl list --namespaces --dimm=DIMM-ID-number

   In the following example, the nmem0 device contains the namespace0.0 and namespace0.2 namespaces, which you need to back up:

   # ndctl list --namespaces --dimm=0
   
   [
     {
       "dev":"namespace0.2",
       "mode":"sector",
       "size":67042312192,
       "uuid":"XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX",
       "raw_uuid":"XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX",
       "sector_size":4096,
       "blockdev":"pmem0.2s",
       "numa_node":0
     },
     {
       "dev":"namespace0.0",
       "mode":"sector",
       "size":67042312192,
       "uuid":"XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX",
       "raw_uuid":"XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX",
       "sector_size":4096,
       "blockdev":"pmem0s",
       "numa_node":0
     }
   ]

6. Replace the broken NVDIMM physically.