1. Mount
Mount - Combine the FSes into one namespace. All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /. These files can be spread out over several devices. The mount command serves to attach the filesystem found on some device to the big file tree. The standard form of the mount command, is mount -t type device dir This tells the kernel to attach the filesystem found on device (which is of type type) at the directory dir. The previous contents (if any) and owner and mode of dir become invisible, and as long as this filesystem remains mounted, the pathname dir refers to the root of the filesystem on device. Unmount - Detaches a previously-attached file system. Divide capacity into multiple "partitions" can have multiple FSes on one disk.
2. Response Time
Response Time = Queue Time + Service Time Service Time = Positioning Time + Transfer Time Positioning Time = Seek + Rotational Time
3. Concepts
Prefetching
Shadow Paging
Write-back caching
Update Ordering
Write-ahead logging
Write amplification writes
Wear leveling writes
4. Integrity mechanisms
In addition to logging writes to NVRAM, modern disk arrays use a variety of other integrity mechanisms. Explain why each of the three mechanisms below is used (1 sentence for each explanation); ECC on memory and bus ECC on memory and bus is used to guard against random bits flipping due to transient failures, solar radiation, etc. Scrubbing data blocks on the disk Scrubbing data blocks in a pro-active way of detecting errors early and (hopefully) correcting them before the data is used. Checksum on each data block Checksumming each data block is used to guard against disk defects that may corrupt data silently.
5. RAID
JBOD
Disk Stripping
Disk Mirroring
Mirroring & Stripping
Parity Disk
6. File Systems
Sprite (Unix)
All reads see most recent write.
NFS(V3)
Other clients' writes visible within 30 seconds.
AFS(V2)
All reads see opened version, which is latest close.