Slides over RAID toegevoegd (gebaseerd op de PPT)

12-RAID.md

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+---
+title: "11.1. RAID"
+subtitle: "Linux<br/>HOGENT toegepaste informatica"
+author: Thomas Parmentier, Andy Van Maele, Bert Van Vreckem
+date: 2023-2024
+---
+
+# RAID - Redundant Array of Independent Disks
+
+## JBOD - Just a Bunch of Disks
+
+![JBOD](assets/raid-jbod.png)
+
+## RAID 0 - Striping
+
+![RAID 0](assets/raid-0-striping.png)
+
+- Secure against single theft
+- Unsecure against hardware failure
+
+## RAID 1 - Mirroring
+
+![RAID 1](assets/raid-1-mirroring.gif)
+
+- Safe against HW failure
+- COMPLETELY unsafe against theft
+    - Use volume encryption! LUKS, Bitlocker, ...
+- Hot spare disk = idle disk, if needed a rebuild action can start automatically
+
+## Parity calculations: XOR
+
+|   A   |   B   | A XOR B |
+| :---: | :---: | :-----: |
+|   0   |   0   |    0    |
+|   0   |   1   |    1    |
+|   1   |   0   |    1    |
+|   1   |   1   |    0    |
+
+## Calculating parity
+
+```text
+data1:  0100 1110
+data2:  1010 1011
+-----------------
+parity: 1110 0101
+```
+
+Recovering data1 using parity:
+
+```text
+data2:  1010 1011
+parity: 1110 0101
+-----------------
+data1:  0100 1110
+```
+
+## RAID 5 - Striping with parity
+
+![RAID 5](assets/raid-5-parity.png)
+
+- At least 3 disks needed
+    - One disk lost for capacity
+- Safe against HW failure of one disk
+    - One disk fails => RAID 0-like situation
+    - If hot spare is configured, rebuild action starts
+    - Warning: increased load on other disks, may trigger other failures
+- Current processors make RAID 5 as fast as RAID 1 (or better!)
+
+## Parity with 4 disks
+
+```text
+block1a:    0100 1110
+block2a:    1010 1011
+---------------------
+parity-tmp: 1110 0101
+block3a:    1101 0011
+---------------------
+parity:     0011 0110
+```
+
+## Recovering block2a using parity
+
+```text
+block3a:    1101 0011
+parity:     0011 0110
+---------------------
+parity-tmp: 1110 0101
+block1a:    0100 1110
+---------------------
+block2a:    1010 1011
+```
+
+## RAID 10 - Mirroring + striping
+
+![RAID 10](assets/raid-10.gif)
+
+- Is RAID 1 (mirroring) combined with RAID 0 (striping)
+- At least 4 disks needed
+    - Half capacity usable!
+- Very frequently used in enterprise environments
+
+## Software vs Hardware RAID
+
+- Difference = where are the calculations done?
+    - HW RAID: dedicated RAID chip (controller - onboard or plugin card)
+    - SW RAID: CPU
+- Directly Attached Storage (DAS): not much use for HW RAID
+    - Main CPU is strong enough for added RAID functionality
+    - Recovery/forensic analysis is easier with SW RAID
+- Network Attached Storage (NAS)/Storage Area Network (SAN): HW RAID
+    - Not much choice, often embedded in the device!
+    - Dedicated RAID controller with proprietary firmware
+
+## The big problem with HW RAID
+
+- Proprietary firmware
+    - In case of data loss: recovery/forensic analysis is difficult/impossible
+- Good RAID controller duplicates config on each disk for recovery purposes
+    - Not a standard! Depends on implementation
+- RAID controllers are *aging*
+    - E.g. RAID 10 on Areca RAID controller is not recognized if the disks are connected to an Adaptec RAID controller
+    - OR: RAID 10 on a 5 year old Areca RAID is not recognized in recend Areca RAID controller
+    - RAID controller has become a single point of failure!
+
+## Software RAID
+
+- Can be done by the OS
+    - Linux Software RAID (mdadm), Linux Volume Management (LVM)
+    - Windows Dynamic Volumes, Storage Spaces
+    - 3rd party software (e.g. Starwind)
+- Usually easily expandable
+- Recoverable
+- Backwards compatible
+- "Free" (included in OS)
+- Independent of interface (IDE, SATA, SCSI, ...)
+- Fast (with modern CPUs)
+
+## Disadvantages of SW RAID
+
+- CPU load
+- OS is not easy to install on a RAID volume
+- Not all RAID levels are supported
+- Hot swap not always supported