Consider a RAID-4 disk configuration involving five disks A, B, C, D and E where disk E stores the parity. Examine the following six scenarios involving read and write operations in the presence of disk failures in this configuration: All disks are up. There is a write operation on block 10 of disk C. Disk B is down and all other disks are up. There is a read operation on block 20 of disk C. Disk C is down and all other disks are up. There is a read operation on block 30 of disk C. Disk D is down and all other disks are up. There is a write operation on block 40 of disk C. Disk E is down and all other disks are up. There is a read operation on block 50 of disk C. Disk E is down and all other disks are up. There is a write operation on block 60 of disk C. In each of the above scenarios determine how many disk accesses happen in order to process the I/O operation. Assume that the goal is to allow as many of the I/O operations as possible, in the presence of disk failures. When counting disk accesses do not count accesses to disks that are down.

File account.java (see previous exercise) contains a definition for a simple bank account class with methods to withdraw, deposit, get the balance and account number, and return a string representation. note that the constructor for this class creates a random account number. save this class to your directory and study it to see how it works. then write the following additional code: 1. suppose the bank wants to keep track of how many accounts exist. a. declare a private static integer variable numaccounts to hold this value. like all instance and static variables, it will be initialized (to 0, since it’s an int) automatically. b. add code to the constructor to increment this variable every time an account is created. c. add a static method getnumaccounts that returns the total number of accounts. think about why this method should be static - its information is not related to any particular account. d. file testaccounts1.java contains a simple program that creates the specified number of bank accounts then uses the getnumaccounts method to find how many accounts were created. save it to your directory, then use it to test your modified account class.