Plex

PLEX:

1. Voulume manager uses sub-disks to build virtual objects called
PLEXES.
2. Is a structured or ordered collection on sub-disks from one or more vmdisk.
3. Cannot be shared by 2 volumes.
4. Maximum number of plexes per volumes is 32
5. Between 2 plexes of same volume mirroring occurs by default.
6. Can have minimum one sub-disk and maximum of 4096 sub-disks
7. 3 types of plexes
a. Complete plex: holds a complete copy of a volume
b. Log plex: dedicated to logging
c. Sparse plex: 1. which is not a compelete copy of the volume
2. Sparse plexes are not used in newer
versions fo voulme manager.
8. Can organixe data on sub-disks to form a plex by using the following
a. Concatenation
b. Striping
c. Mirroring
d. Striping with parity


Plex states:
1. If a disk with a particular plex located on it begins to fail, we can temporarily disable the plex.
2. Vxvm utilities automatically maintains the plex state.
Vxvm utilities uses the plex states for the following
a. Indicate whether volume contents have been initialized to a known state
b. Determine if a plex contains a valid copy (mirror) of the volume contents
c. Track whether a plex was in active use at the time of a system failure
d. Monitor operations of plex.

3. States of plex:
There are 15 states of plex available
a. Active plex state:
- On a system running level, ACTIVE should be the most common state, we can observe for any volume plex.
- Can be in the ACTIVE state by 2 ways
i. When the volume is started and the plex fully participates in normal volume I/O, the plex contents change as the contents of the volume change.
ii. When the volume is stopped as a result of system crash and the plex is ACTIVE at the moment of crash.
- In the later case, a system failure can leave plex contents in a consistent state. When a volume is started, Vxvm does the recovery action to guarantee that the contents of the plexes are marked as ACTIVE are made identical.
b. Clean plex state:
- Known to contain a consistent copy (mirror) of the volume contents & an operation has disable the volume.
c. DCOSNP plex state:
- Indicates that the DCOSNP (Data Change Object SNaPshot plex) attached to a volume can be used by a snapshot plex to create a DCO volume during snapshot operation.
d. Empty plex:
- Indicates that this plex are not initialized.

e. IOFAIL plex:
- Occurs when vxconfigd daemon detects an un correctable I/O error.
- It is likely that one/more of the disks associated with the plex to be replaced.

f. Log plex:
- The state of DRL – Dirty Region Log is always set to log plex.
g. Offline plex:
- Although the detached plex maintains its association with the volume, changes to the volume do not update the offline plex. The plex is not updated until the plex is put alive and re-attached.
h. SNAPATT plex:
- Indicates a snapshot plex that is being attached by snapshot (beginning) operation.
- Note: If the system fails before the attach completes, the plex & all of its sub-disks are removed.
i. SNAPDIS plex:
- Indicates a snapshot plex is fully attached.
j. SNAPDONE plex:
- Once the snapshot is completely achieved.
k. SNAPTMp plex:
- When a snapshot is being prepared on a volume.
l. STALE:
- If there is possibility that a plex does not have the complete & current volume contents, that plex is placed in STALE state.
- If an I/O error occurs on a plex, the kernel stops using & updating the contents of that plex and the state is STALE.
- Note 1: # vxplex att
Operation recovers the contents of a STALE plex from an ACTIVE plex.
- Note 2: # vxplex det
Root-user can executes the above command to bring the plex to STALE state.
m. TEMP plex:
- Indicates that the operation is incomplete.
n. TEMPRM plex:
- Similar to TEMP plex, but except that the completion of the operation, TEMPRM plex is removed.
o. TEMPRMSD plex:
- Occurs when attaching new data plexes to a volume.
- If the sync operation does not complete, the plex and its sub-disks are removed.

Plex condition flags:
1. IOFAIL plex condition
2. NODAREC plex condition
3. NODEVICE plex condtion
4. RECOVER plex condition
5. REMOVED plex condition

Plex kernel states:
No user intervention is required to set these states, they are maintained internally. On a system that is operating properly, all plexes are enabled.
DETACHED plex kernel state:
- Maintenance is being performed on the plex.
- Any write request to the volume is not reflected in the plex.
- Read request from the volume is not satisfies from the plex.
DISABLED ples kernel state:
- The plex is offline & cannot be accessed.
ENABLED plex kernel state:
- Plex is online.
- Any write request to the volume is reflected on the plex.
- Read request from the volume is satisfied from the plex.

ADMINSTERING PLEX:

1. Creating the plex
2. Viewing the plexormation
3. Associating the plexh the volume
4. Dissociating the plex from the volume
5. Deleting the plex

Creating a plex:

Output:

bash-3.00# vxmake -g oradg plex oradgvol1-01 sd=oradg02-04,oradg02-05

bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol1-01 - DISABLED - 8388608 CONCAT - RW
pl oradgvol01-01 - DISABLED - 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW



Viewing plex information:

bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol1-01 - DISABLED - 8388608 CONCAT - RW
pl oradgvol01-01 oradgvolume DISABLED EMPTY 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW
bash-3.00# vxplex -g oradg att oradgvolume oradgvol1-01
bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol1-01 oradgvolume DISABLED EMPTY 8388608 CONCAT - RW
pl oradgvol01-01 oradgvolume DISABLED EMPTY 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW


bash-3.00# vxprint -g oradg -l oradgvol01-01
Plex: oradgvol01-01
info: len=2097152
type: layout=CONCAT
state: state= kernel=DISABLED io=read-write
assoc: vol=(dissoc) sd=oradg02-02
flags:



Associating plex to volume:

Output:


Case-1:


bash-3.00# vxplex -g oradg att oradgvolume oradgvol1-01

bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol1-01 oradgvolume DISABLED EMPTY 8388608 CONCAT - RW
pl oradgvol01-01 oradgvolume DISABLED EMPTY 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW


Case-2:

bash-3.00# vxmake -g oradg -U fsgen vol oradgvolume plex=oradgvol01-01
bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol1-01 - DISABLED - 8388608 CONCAT - RW
pl oradgvol01-01 oradgvolume DISABLED EMPTY 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW




bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol1-01 oradgvolume DISABLED EMPTY 8388608 CONCAT - RW
pl oradgvol01-01 oradgvolume DISABLED EMPTY 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW


Dissociating/Deleting the plex:

Output:

Case-1:


bash-3.00# vxplex -g oradg det oradgvol1-01
bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol1-01 oradgvolume DETACHED EMPTY 8388608 CONCAT - RW
pl oradgvol01-01 oradgvolume DISABLED EMPTY 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW


Case-2:

bash-3.00# vxplex -g oradg -o rm dis oradgvol1-01
bash-3.00# vxprint -g oradg -pt
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE

pl oradgvol01-01 oradgvolume DISABLED EMPTY 2097152 CONCAT - RW
pl vol1-01 vol1 ENABLED ACTIVE 4194304 CONCAT - RW