27-07-2012, 04:14 PM
Mass-Storage Structure
[attachment=29315]
Disk Attachment
Host-attached storage
Storage accessed on host through local I/O port
Uses hardware bus and host controller (e.g., IDE, ATA, SATA, FireWire, USB, SCSI, FC– Fiber Channel)
Network-attached storage
Special purpose storage system attached remotely over a data network
Clients access severs via RPC (e.g., NFS for Unix systems or CIFS for Windows systems)
Storage-area network
Private network (using storage protocols) connecting file servers and storage units
Erase and SSD
Erase: Writing to the SSD must be preceded by a block erase (sets all bits to 1)
Lifetime: Measured in the number of erase cycles
Wear leveling: Firmware or operating system drivers must balance the numbers of erase cycles done on each block so that device does not fail prematurely
SSD Performance
Single chip has relatively high latencies (SLC NAND)
~25 μs to fetch (read) a 4K page from the array to the IO buffer
~250 μs to commit (write) a 4K page from the IO buffer to the array
~2 ms to erase a 256 kiB block
With parallel chip operation, 250 MB/s effective read/write speeds
FCFS Performance Issues
It is possible for disk positions far from a current area of activity to be starved indefinitely?
No. With FCFS, incoming (new) requests will eventually get processed.
We are not reordering requests here.
The algorithm is intrinsically fair, but it generally does not generally provide the fastest service.
[attachment=29315]
Disk Attachment
Host-attached storage
Storage accessed on host through local I/O port
Uses hardware bus and host controller (e.g., IDE, ATA, SATA, FireWire, USB, SCSI, FC– Fiber Channel)
Network-attached storage
Special purpose storage system attached remotely over a data network
Clients access severs via RPC (e.g., NFS for Unix systems or CIFS for Windows systems)
Storage-area network
Private network (using storage protocols) connecting file servers and storage units
Erase and SSD
Erase: Writing to the SSD must be preceded by a block erase (sets all bits to 1)
Lifetime: Measured in the number of erase cycles
Wear leveling: Firmware or operating system drivers must balance the numbers of erase cycles done on each block so that device does not fail prematurely
SSD Performance
Single chip has relatively high latencies (SLC NAND)
~25 μs to fetch (read) a 4K page from the array to the IO buffer
~250 μs to commit (write) a 4K page from the IO buffer to the array
~2 ms to erase a 256 kiB block
With parallel chip operation, 250 MB/s effective read/write speeds
FCFS Performance Issues
It is possible for disk positions far from a current area of activity to be starved indefinitely?
No. With FCFS, incoming (new) requests will eventually get processed.
We are not reordering requests here.
The algorithm is intrinsically fair, but it generally does not generally provide the fastest service.