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/All/ processes that read from or write to an NFS mounted filesystem can block (until the I/O operation completes) for long periods of time. If that happens then whatever resources or locks that process owns are not available to other processes. In the worst case, this can lead to all programs connected to the database becoming blocked. for example, an online backup that is writing the backup to an NFS filesystem can block on a write. then any process that wants to update a database block that has not yet been backed up will queue the block for backup and wait for it before proceeding to perform the update. Since the backup program is blocked, it is not servicing the queue. the After-Image archiving daemon can block too. This can lead to all the ai extents becoming full so there is no room left to write new after-image log records. This behaviour can occur with other types of storage devices too, even direct attached disk drives, but is much, much less likely.
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