This file contains some important notes on upgrade process.

* Upgrading to LizardFS 3.10.0:
    Direct upgrade is possible from LizardFS 2.6.0 - 3.9.4.
    - For upgrade from LizardFS 2.6.0, see upgrade notes for LizardFS 3.9.2
    - Upgrade shadow master servers before the master server; shadow master will always
      refuse to connect to the master server in any newer version.
    - Upgrade the master/shadow servers before any chunkserver or client.
    - Chunkservers should be updated before clients, as they can still understand legacy
      mount requests. Updating a client first will result in being unable to read from/write to
      a 2.6.0 chunkserver.
    - Neither master servers nor chunkservers have hard coded connection limit anymore.
      The previous value were 5000 for master server and 10000 for chunkserver.
      It is advisable to check if system limits are high enough for proper work of LizardFS cluster.
      Mentioned values can be changed by modifying /etc/security/limits.d/10-lizardfs.conf
      file or by using ulimit command.

* Upgrading to LizardFS 3.9.4:
    Direct upgrade is possible from LizardFS 3.9.2 and LizardFS 2.6.0.
    - 3.9.2 chunkservers need to be upgraded ASAP due to protocol changes
    - See upgrade notes for LizardFS 3.9.2

* Upgrading to LizardFS 3.9.2:

    Direct upgrade is possible from LizardFS 2.6.0.

    - Upgrade shadow master servers before the master server; shadow master will always
      refuse to connect to the master server in any newer version.
      !!!!!!!!!! ATTENTION !!!!!!!!!!!!!!! ATTENTION !!!!!!!!!!!!!!!! ATTENTION !!!!!!!!!!
      ! It is recommended to perform metadata save before upgrading shadow servers       !
      ! and refrain from using mfsmakesnapshot tool before upgrading master.             !
      ! Not complying to this rule might cause potential checksum mismatches in shadows. !
      ! Metadata save can be triggered by admin tool:                                    !
      ! $ lizardfs-admin save-metadata HOST PORT                                         !
      !!!!!!!!!! ATTENTION !!!!!!!!!!!!!!! ATTENTION !!!!!!!!!!!!!!!! ATTENTION !!!!!!!!!!
    - Upgrade the master/shadow servers before any chunkserver or client.
    - Chunkservers should be updated before clients, as they can still understand legacy
      mount requests. Updating a client first will result in being unable to read from/write to
      a 2.6.0 chunkserver.
    - Neither master servers nor chunkservers have hard coded connection limit anymore.
      The previous value were 5000 for master server and 10000 for chunkserver.
      It is advisable to check if system limits are high enough for proper work of LizardFS cluster.
      Mentioned values can be changed by modifying /etc/security/limits.d/10-lizardfs.conf
      file or by using ulimit command.

* Upgrading to LizardFS 2.6.0:

    Direct upgrade is possible from:
    - MooseFS  1.6.27 -- 1.6.27-5
    - LizardFS 1.6.28 -- 2.5.4.3

    When upgrading from LizardFS 2.5.4 or 2.5.4.*
    - Upgrade shadow master servers before the master server; shadow master will always
      refuse to connect to the master server in any newer version.
    - Upgrade the master server before any chunkserver or client.

    When upgrading from LizardFS 2.5.0 or 2.5.2
    - Proceed the same as in case of upgrade to LizardFS 2.5.4.

    When upgrading from other releases:
    - Proceed the same as in case of upgrade to LizardFS 2.5.2.

* Upgrading to LizardFS 2.5.4:

    Direct upgrade is possible from:
    - MooseFS  1.6.27 -- 1.6.27-5
    - LizardFS 1.6.28 -- 2.5.2

    When upgrading from LizardFS 2.5.0 or 2.5.2:
    - Upgrade shadow master servers before the master server; shadow master will always
      refuse to connect to the master server in any newer version.
    - Upgrade the master server before any chunkserver or client.
    - Clients, chunkservers and the master server can be upgraded in any order (all of them
      are compatible with each other), either one by one or all at once.
    - CGI server 2.5.4 is compatible with all versions of the master server (1.6.27 -- 2.5.2),
      so it can be upgraded at any time. Because of a bug in older versions of the CGI server
      it has to be stopped manually before being upgraded (otherwise installation of the newer
      package may fail).

    When upgrading from other releases:
    - Proceed the same as in case of upgrade to LizardFS 2.5.2.

* Upgrading to LizardFS 2.5.2:

    Direct upgrade is possible from:
    - MooseFS  1.6.27 -- 1.6.27-5
    - LizardFS 1.6.28 -- 2.5.0

    When upgrading from LizardFS 2.5.0:
    - Upgrade shadow master servers before the master server; shadow master will always
      refuse to connect to the master server in any newer version.
	- Upgrade the master server
    - Clients, chunkservers and the master server can be upgraded in any order (all of them
      are compatible with each other), either one by one or all at once.

    When upgrading from previous releases:
    - There is no possibility to use shadow masters 2.5.2 before upgrading the master server.
    - Upgrade the master server first, then all the chunkservers and then clients (either all
      at once or one by one).

* Upgrading to LizardFS 2.5.0:

    Direct upgrade is possible from:
    - MooseFS  1.6.27 -- 1.6.27-5
    - LizardFS 1.6.28

    Master server has to be upgraded before any client.
    Chunkservers can be upgraded in any order (before the master server is upgraded or after).
    Shadow master server 2.5.0 is compatible with master server 1.6.27 and newer.

* Upgrading to LizardFS 1.6.28:

    Direct upgrade is possible from:
    - MooseFS 1.6.27 -- 1.6.27-5.

    All the servers and clients are compatible and can be upgraded in any order.
