requirements docs improved with missing information fixed

prerequisites.rst

@@ -1,35 +1,275 @@
-Prerequisites
+Requisites
 =============
 
-Before installing |omv| make sure your hardware is supported.
+The |omv| system is the most flexible Network Attached Storage (NAS) on the market,
+this is because it relies on the operating system Debian GNU/Linux [9]_
 
-* **CPU**: Any x86-64 or ARM compatible processor
-* **RAM**: 1 GiB capacity
-* **HDD**:
+Any system has software and hardware requirements, also minimal
+ones and recommended ones.
 
-  * **System Drive**: min. 4 GiB capacity (plus the capacity of the RAM)
-  * **Data Drive**: capacity according to your needs
+Hardware requirements
+---------------------
 
-.. note::
-   The whole disc will be occupied by the system and swap space [1]_, so size
-   doesn't matter so much. Data storage on the system disc is not supported.
+======  ================  =========  ==========  ==================================
+ Item    supported         Minimal     Best       Recommendation
+======  ================  =========  ==========  ==================================
+ DRIV    SSD/HDD/USB...     1,any      2,HHD      2 disks: Seagate Firecuda, WD Black, IronWolf
+ RAM     1GiB+ any          1GiB       4Gig       8GiB+ dual channel DDR4/DDR3
+ NIC     WiFi/Ether/USB     any       10Mb NIC    1GiB NIC or 10Gb NICs: SFP fiber
+ CPU     arm,x86,x64        32bit      64bit      Intel Dual Core, AMD Ryzen
+======  ================  =========  ==========  ==================================
 
-.. note::
-   Take into account in your considerations about the size of the system disk
-   that various plugins such as `openmediavault-podman` or `openmediavault-k8s`
-   store their data (e.g. container images) on the system disk.
+The storage drives (DRIV)
+^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Spinning Harddisk, SSD [2]_, Disk-on-Module [3]_, CompactFlash [4]_ or USB thumb
-drive [5]_ type drives can be used as system drive.
+This is the key of the system. |omv| supports any drive hardware and any drive 
+interface (SATA, ISE, SCSI, USB, SERIAL) but information and management will
+depend on the disk drives supported by the Debian operating system.
+**Supported Debian OS versions can be checked in the** :doc:`releases section </releases>`.
+
+Modern storage drives have firmware inside that reports several attributes.
+Any storage drives is supported but |omv| only supports SMART for those
+disks that are connected to an HBA in pass-through mode.
+
+The system manages two types of storage unit classification:
+
+System drive storage (SDS)
+  The Storage Disk Drive(s) used to put the system program files. 
+  **This system drive (which can consist of several partitions) 
+  cannot officially be used for shared resources or as user data drive**.
+  The recommendation for the system drive(s) hardware could be older spinning
+  Hard Disk Drives (HDD), Disk-on-Module [3]_, CompactFlash [4]_ or thumb drives (USB),
+  the Solid State Disks (SDD [2]_) must be managed. Best option are 
+  the Helium Hard Drives (HHD).
+
+Data drive storage (DDS)
+  The storage disk drive(s) where the user data will be stored. **Cannot be 
+  the same of the system drive(s) and sizes will depend of the usage of the stored user data**.
+  Shared resources are managed over partitions, which is discussed in the software
+  requirements topic below. The recommendation for the Data drives must be
+  Solid State Disks (SSD [2]_ disks) for best performance or spinning 
+  Hard Disk Drives (HDD) for better device durability over time.
+
+The memory (RAM)
+^^^^^^^^^^^^^^^^
+
+Enough RAM is vital to maintaining peak performance. There are several combinations
+of installation sizes but the **recommendation is at least 4GiB for novice administrators**.
+
+For best practice you should have 8GiB of RAM for basic operations in default installation,
+and no matter the size, RAM must be configured in Dual Channel mode [8]_ 
+inclusivelly if there are little amount of, it will improve performance.
+
+Unless other NAS systems the |omv| system can run in at least 1GiB of RAM, but
+of course will need expertise.
+
+The communication card (NIC)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+A NAS system as means is a network oriented system, of course |omv| is the
+most flexible NAS system in the world and allows multiple ways of communication, 
+this is becouse |omv| offers several modes of shared resources like RSYNC that 
+do not depends on networking. But there are few key points:
+
+- The NAS write speed to storage is limited to the speed of your NAS computer NIC card.
+- The NAS write speed to storage is limited to the speed of your network.
+- Speed of writing to the storage depends on ratio of the number of users accessing it.
+
+Full-duplex NICs are recommended, half-duplex NICs typically offer 10/100 Mbit/s
+and storage drives far exceed those speeds but are of course supported by |omv|.
+
+Any supported NIC vendor is determined by the support of the operating system
+where |omv| system resides and runs, which is Debian GNU/Linux.
+
+The architecture (CPU)
+^^^^^^^^^^^^^^^^^^^^^^
+
+We have already denoted in the requirements table the supported architectures or
+processors (which reduces and determines which computers can be used) but this is
+really a reference since it is determined by the support of the operating system
+where |omv| system resides and runs, which is Debian GNU/Linux.
+
+Any computer system supported by the common requirements of Debian operating
+system could be an |omv| system installation target. **Currently supported are
+AMD64 (x86/x86-64 64bits), i386 (x86 32bits), ARMv7+ARMv8 (arm64 64bits armel/armhf 32bits)**.
+The i386 version is no longer officially supported since version 6, although
+it is still published by the project due to the nature of |omv| technology.
+
+Software requirements
+---------------------
+
+======  =================  ==============  ================  =========================================
+ Item    Software           Minimal         Best              Recommendation
+======  =================  ==============  ================  =========================================
+ OS      Debian Linux       oldstable       stable            Current stable (plus 1 month released)
+ BOOT    BIOS,UBOOT,UEFI    BIOS,mbr        BIOS,gpt          Disable Secure boot, gpt table
+ SDS     HDD,SSD,USB...     1, 4GiB         2, 120+500GiB     Disk drive with 120G root size, 8G swap size
+ DDS     HDD,SSD,USB...     0 or any        HHD,1 per share   One disk or part per shared resource
+ NET     LAN,WAN,SAN,VPN    LAN             SAN,PAN,LAN       Fiber IPv4, or at least cable LAN
+======  =================  ==============  ================  =========================================
+
+The operating system (OS)
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The |omv| is a piece of software, it resides and runs under a key software OS
+named Debian GNU/Linux as "the universal operating system" [9]_ 
+
+**Supported Debian OS versions can be checked in the** :doc:`releases section </releases>`.
+
+While possible to deploy in a virtual environment, depending of the nature of
+virtualization it will degrade the performance access in various ways. Installation
+in LXC or any other container based solution is not supported.
+
+Whatever the situation, the |omv| assumes that target operating system does not
+have any previous installation of any of the programs used by |omv| dependencies:
+
+=============  ==============  =================  ==========================================
+ software       package          related to        Observations
+=============  ==============  =================  ==========================================
+ http server    nginx           |webui|            port 80 must be free at installation
+ http system    php             |webui|            only OS php packages wil be used!
+ display GUI    lighdm,xdm..    Desktop install    **Conflicts, any will be deinstalled**
+ network man    netplan.io      Networking         network is managed by |omv| with netplan
+ ssh server     ssh             Remote access      any configuration will be managed
+ smb server     samba           Shared drives      any configuration will be managed
+ quota man      quota           Quota manage       any configuration will be managed
+=============  ==============  =================  ==========================================
+
+The device boot (BOOT)
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The boot type and its support is determined by the Debian operating system
+which supports BIOS, UEFI, PXE, UBOOT and many others, the configurations
+of these depend on the installation of the operating system and once done
+the |omv| can be installed without problems.
+
+However the downloadable and ready-to-use ISO image from the official |omv| website
+only supports AMD64 with BIOS mode boot at the moment. If you want to have |omv| on
+other computers with another boot type/mode, then you should install Debian first
+and then :doc:`manually</installation/on_debian>` |omv|.
+
+**Supported Debian OS versions can be checked in the** :doc:`releases section </releases>`.
+
+The system drive storage (SDS)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Any brand of storage disk will be supported as long as it is supported by
+the Debian operating system version, since it is where |omv| system resides
+and runs, which is Debian GNU/Linux, check it at the :doc:`releases section </releases>`.
+
+The system storage disk will be fully managed and taken over by |omv| after
+installed. In case of the official ISO installation, will automatically partition
+the system storage disk drive into 3 partitons. Consult the next table for.
+
+In case of a manual installation on a previous Debian operating system, this
+**drive should have at least two partitions**. Consult the next table for.
+
+============  ==========  ===========  =======================================
+ Partition     Mininmal    Best size    Mandatory
+============  ==========  ===========  =======================================
+ ``/boot``      256Mib      500Mib      Optional, partition used to boot
+ ``/``           4Gi        120GiB      Yes, the partition were system install
+ ``swap``       100Mib      16GiB       Optional, the partition for virtual ram
+============  ==========  ===========  =======================================
+
+The Data drive storage (DDS)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The data storage disk will be partially managed by the |omv| after installation,
+and only in customized installation this can be a partition of the same system drive
+storage.
+
+Each data storage drive will be managed, but regardless of the partitioning
+scheme, all data drive partitions will be mounted at the ``/srv/`` path.
+The **data storage drive must be a different disk drive than the system disk drive**
+where the operating system is installed. **One partition of each data
+drive can handle one or many shared resources.**
+
+==============  ==========  ===========  ========================================
+ Partition       Min size    Best size    Mandatory
+==============  ==========  ===========  ========================================
+ ``/srv/<*>``     100Mib       bigger     Yes, size as need! E.g. 128GiB,500GiB,4TiB
+==============  ==========  ===========  ========================================
+
+Technical notes
+---------------
+
+Take into **consideration that as more exquisite the customization as less supported
+could be.**.
+
+|omv| allows for minimal deployment and use of the system with very minimal
+hardware/software requirements, at the cost of the key knowledge, but other NAS
+systems allow ease of use at the cost of high requirements. |omv| allows both as
+well in a well balanced use case! [7]_
+
+About minimal or custom setups
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+It can be noted that |omv| systems can be installed on just 4GiB of system partition,
+with no more than 1GiB of RAM and using a WiFi or USB connection to access it
+remotely, on any small device such as Raspberry Pi or Banana Pi boars
+which are ARM, or old i386s machines no matter is those are 32 or 64 bits, 
+but of course as more exquisite the configuration more knowledge will be need
+as per `issue comment #131 <https://github.com/openmediavault/openmediavault-docs/issues/131#issuecomment-2546765841>`_.
+
+Technically OMV can be installed on a single storage disk, this is possible if
+it is done on a previously configured Debian system, with a free partition apart
+from the 3 necessary system partitions, previously formatted and configured.
+Of course this is only possible for skilled Linux users.
+
+Drive Storage technical details
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+System Drives are not managed as same of Data Drives. System drives are not so
+intensively used, but Data Drives will need tricks to extend the useful life.
+Drivers support is by the project https://www.smartmontools.org/wiki/TocSupport
+
+If you use a Flash Drive, select one with static wear leveling 6, without this
+the drive will have a very short lifetime. It is also recommended to install and
+activate the Flash Memory plugin.
+
+In the same Solid State Disk, or rather Drive (SSD) for x86 based architectures, is
+usually only recognized properly by the BIOS or UEFI, when in the BIOS/UEFI the
+feature AHCI has been activated for SATA (instead of IDE). Modern computers have that
+by default. But on old machines the default might/could be IDE.
+About ARM based computers this is not a problem, when used SATA interfaces, but
+on eMMCs will need some tuning because they are treated like Flash drives.
+
+On SSDs, the cleaning action TRIM is recommended for the good performance in
+the long run. Otherwise it might become slow after some time. Very old SSD's from
+before 2010 usually don't support TRIM.
+
+Take note that eMMCs, SSDs, Flash drives will have a lifetime degradation, 
+excessive overwrites wear out those drives faster, specially in those very cheap.
+
+On SSDs Hibernation (suspend-to-disk) causes a huge amount of write actions,
+|omv| is a server system so it is expected to stay always on or off.
+
+About compresion or encryption
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Enabling encryption on SSDs also means more overwrites which wear out SSDs, eMMCs
+or Flash drives faster.
+
+As well as enabling compression on filesystems like Btrfs or ZFS; although Ext4
+has better commit timing; a parameter with commit=600 to 800 is best
+for this particular one.
+
+Partition table technical details
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Of course, the supported partition tables will depend on the installation mode,
+and |omv| can handle any type of partition table supported by the Debian operating
+system. This is because to manage shares on new or uninitialized storage drives
+it will need to create partitions or at least read structure of thems.
 
-If you use a Flash Drive, select one with static wear leveling [6]_, without
-this the drive will have a very short lifetime. It is also recommended to
-install and activate the :ref:`Flash Memory plugin <plugin_3rd_party>`. The
-entire disk is used as system disk and can not be used to store user data.
 
 .. [1] https://en.wikipedia.org/wiki/Paging
 .. [2] https://en.wikipedia.org/wiki/Solid-state_drive
 .. [3] https://en.wikipedia.org/wiki/Solid-state_drive#DOM
 .. [4] https://en.wikipedia.org/wiki/CompactFlash
 .. [5] https://en.wikipedia.org/wiki/USB_flash_drive
 .. [6] https://en.wikipedia.org/wiki/Wear_leveling
+.. [7] https://forum.openmediavault.org/index.php?board/29-guides/
+.. [8] https://en.wikipedia.org/wiki/Multi-channel_memory_architecture
+.. [9] https://www.debian.org/intro/about.en.html#what