Solid State/Magnetic/Optical Storage
Host Interfaces
Allow the device to be attached to the processor. Important considerations are bandwidth and command overhead.
- PCI
- PCIe
- CardBus
- USB
- Ethernet
Storage Device Interfaces
Provide a standard protocol for communicating with the host interface adapters.
Native Device Interfaces
Low level interface with commands mapping directly to device functions
- SATA serial ATA
- PATA parallel ATA
- ESATA external serial ATA
- iATA (ATA via ethernet tcp/ip)
- SCSI-1
- SCSI-2
- SCSI-3
- iSCSI (SCSI via ethernet tcp/ip) (note - 3 generations of SCSI varying in data width and speed with associated cabling including termination variations.)
High Level Interfaces
Embedded controller translates the native device interface to a higher level protocol such as USB or Ethernet allowing easier integration with Host device drivers.
- USB Storage
- Network Storage
Types of Storage Media
- Rotating memories
- Optical
- Magnetic
- Solid State
- Volatile
- SRAM static RAM
- DRAM dynamic RAM (SDRAM, DDRAM)
- Non-Volatile
- NAND Flash
- NOR Flash
- Hybrid combinations of above
Device Characteristics
Performance
Access Time
- In the case of rotating memory devices, access time is a result of seek and latency times (i.e. seeking to a cylinder(seek time) and wait for the sector to arrive at the data head (latency time)). The faster the RPM, the lower the latency time, eg. 7200 RPM is approximately 8 milliseconds per rotation.
- For NAND flash, access time includes addressing and waiting for the block and then sequencing through the bytes until the desired byte is available.
Transfer Time
- Burst transfer rate is the instantaneous (i.e. maximum) rate.
- Sustained transfer rate is the average over a long period of time, it accounts for such interruptions in the data flow as error correction or crossing cylinder boundaries where the disk arm must seek to the next cylinder.
- Transfer rate might be limited by the host interface, eg. most media is capable of exceeding the basic transfer rate of USB-1 which is 1.2 megabits per second.
- Transfer rates are also affected by the cacheing, especially sustained rates are markedlly improved with cacheing depending on the work loads.
Read and Write Time Variances
- For some memory types, it is necessary to erase and write one entire block at a time. Therefore, random access writes would be very slow on a NAND flash device.
Price
- to be discussed
Data Retention
Factors affecting Life-time of inactive media
Factors affecting Life-time of active media
- limited # of write cycles
- heat degradation
- mechanical failure
Power Consumption
- to be discussed
Error Correction
- to be discussed
Multiple Device Organization
RAID
- redundancy
- speed
- hot-swap
LVM
- to be discussed
