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  • Storage Systems

    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.

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  • 原文地址:https://www.cnblogs.com/null00/p/3041696.html
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