raid and erasure coding

lectures/file-and-data-systems/slides.qmd

@@ -320,16 +320,37 @@ mv same_same_but_different slides.qmd
 
 # Redundancy
 
-## RAID 
-
-## Erasure coding 
-
+Can protect against
+* Accidental deletion
+* Protection against data loss
+* High Availability
+
+## Backups
+* Keep old states of the file system available
+* Need at least as much space as the (compressed version of the) data being back-uped.
+* Ideally at different locations.
+* Automate them!
+
+## RAID
+
+* Combining multiple harddisks into bigger / more secure combinations
+* RAID 0 distributes the blocks across all disks - more space, but data loss if one fails.
+* RAID 1 mirrors one disk on an identical copy.
+* ...
+* RAID 5 is similar to 0, but with one extra disk for (distributed) parity info
+* RAID 6 is similar to 5, but with two extro disks for parity info (levante uses 8+2 disks).
+p
+## Erasure coding
+
+* Similar to raid, but more flexible with the numbers of disks (more than two *parity* disks are possible).
+* Used in object stores
+* Usually, data is distributed across independent servers for higher availability.
 
 # Lustre as a parallel file system
 
 *What if you are not the only one controlling the FS?*
 
-. . . 
+. . .
 
 The file system becomes an independent system.