what is a plex

[ Edited ]

what is a plex ?

Re: what is a plex


It is a term used with regards to a mirrored aggregate (via SyncMirror) which has two plexes:

SyncMirror protects against data loss by maintaining two copies of the data contained in the aggregate, one in each plex.



Re: what is a plex

By default all your raidgroups will be tied towards plex0, the moment you enable syncmirror things will change. After enabling the syncmirror license you move disks from default pool pool0 to pool1. Then when you syncmirror your aggregate you will find pool0 disks will be tied with plex0 and pool1 will be under plex1.



Re: what is a plex

A plex is a physical copy of the WAFL storage within the aggregate. A mirrored aggregate consists of two plexes; unmirrored aggregates contain a single plex.


Re: what is a plex

I hate to bring up an old topic again, but this looks like it still has no correct answer.

I am trying really hard to find out what a plex actually is or a document with some information on it.  From the previous replies it looks like it is a copy of the aggregate, however I am not really understanding where that information would be stored or how it really works.  Can someone provide a little more information on what a plex is?



Re: what is a plex

A plex is a physical copy of a filesystem or the disks holding the data. A DataONTAP volume normally consists of one plex.   A mirrored volume has two or more plexes, each with a complete copy of the data in the volume.  Multiple plexes provides safety for your data as long as you have one complete plex, you will still have access to all your data.


Re: what is a plex

Thank you for the reply Doug.

I understand a little more now, but I am still a little lost on where the plex exists.

Lets say I create four (4) volumes all in one aggregate I end up with four (4) plexes correct?  If that is correct does that mean if I create a Volume of 500GB and then create a LUN of 250GB, I need to have that left over 250GB as space for the plex?



Re: what is a plex

A plex is on top of aggr, raid groups reside on top of plexes, volumes reside in raid groups.  There can be several raid groups to a single plex.  You can only have 1 mirror of a plex in ONTAP 7.

To view plex info:

aggr status -v
            Aggr State           Status            Options
           aggr0 online          raid0, aggr       root, diskroot, nosnap=off,
                                                   raidtype=raid0, raidsize=8,

                Volumes: vol0

                Plex /aggr0/plex0: online, normal, active
                     RAID group /aggr0/plex0/rg0: normal

vol status -v
         Volume State           Status            Options                     
           vol0 online          raid0, flex       root, diskroot, nosnap=off, 
                                                  nosnapdir=off, minra=off,
                                                  no_atime_update=on, nvfail=off,
                                                  guarantee=volume, svo_enable=off,
                Containing aggregate: 'aggr0'

                Plex /aggr0/plex0: online, normal, active
                    RAID group /aggr0/plex0/rg0: normal

        Snapshot autodelete settings for vol0:
                                        prefix=(not specified)
        Volume autosize settings:

From man na_aggr (maybe this will help):

A plex is a physical copy of the WAFL storage within the aggregate. A mirrored aggregate consists of two plexes; unmirrored aggregates contain a single plex. In order to create a mirrored aggregate, you must have a filer configuration that supports RAID-level mirroring. When mirroring is enabled on the filer, the spare disks are divided into two disk pools. When an aggregate is created, all of the disks in a single plex must come from the same disk pool, and the two plexes of a mirrored aggregate must consist of disks from separate pools, as this maximizes fault isolation. This policy can be overridden with the -f option to aggr create, aggr add and aggr mirror, but it is not recommended.

A plex may be online or offline. If it is offline, it is not available for read or write access. Plexes can be in combinations of the following states:

normal All RAID groups in the plex are functional.

failed At least one of the RAID groups in the plex has failed.

empty The plex is part of an aggregate that is being created, and one or more of the disks targeted to the aggregate need to be zeroed before being added to the plex.

active The plex is available for use.

The plex is not available for use.

The plex's contents are currently out of date and are in the process of being resynchronized with the contents of the other plex of the aggregate (applies to mirrored aggregates only).

adding disks
Disks are being added to the plex's RAID group(s).

This state only occurs in mirrored aggregates where one of the plexes has failed. The non-failed plex will be in this state if it needed to be resynchronized at the time the other plex failed.

A plex is named using the name of the aggregate, a slash character delimiter, and the name of the plex. The system automatically selects plex names at creation time. For example, the first plex created in aggregate aggr0 would be aggr0/plex0.

The disks in a plex are not permitted to span disk pools. This behavior can be overridden with the -f flag when used together with the -d argument to list disks to add. The -f flag, in combination with -d, can also be used to force adding disks that have a rotational speed that does not match that of the majority of existing disks in the aggregate.

The -m option can be used to specify that the new aggregate be mirrored (have two plexes) upon creation. If this option is given, then the indicated disks will be split across the two plexes. By default, the new aggregate will not be mirrored.

If you use the -d disk1 [ disk2 ... ] argument, the filer creates the aggregate with the specified spare disks disk1, disk2, and so on. You can specify a space-separated list of disk names. Two separate lists must be specified if the new aggregate is mirrored. In the case that the new aggregate is mirrored, the indicated disks must result in an equal number of disks on each new plex.

The disks in a plex are not permitted to span spare pools. This behavior can be overridden with the -f option. The same option can also be used to force using disks that do not have matching rotational speed. The -f option has effect only when used with the -d option specifying disks to use.

Re: what is a plex

Doug, you are awesome.  That is exactly the information I needed to understand.

Thanks again!

Re: what is a plex

Hello Geniuses,

I am in bit of doubt and ambiguity about max mumber of plex can be in one aggregate. Untill few hours back I knew that one aggregate mean 1 plex. But when somehow (hardly ) I opened FilerView help and read that :

  1. You can create a mirrored aggregate in the following ways:
    • You can create a new aggregate that has two plexes.

    • You can add a plex to an existing, unmirrored aggregate.

  2. An aggregate cannot have more than two plexes.

So my question is:

  1. In a Single aggregate (unmirrored) can have more than one plex?
  2. What exactly plex contain? (like I understand RAID contain RAID configuration).

Many thanks in advance...