Disk Storage Systems

Disk Storage Systems

1. Rotational media

   • Fixed
     • HDD
       • 3.5 inch
       • 2.5 inch (laptop)
       • random data access
   • Removable
     • CD, floppy, USB drive
     • flash memory card
   • Electronic, magnetic, optical, mechanical

2. Interface

   • Advanced Technology Attachment (ATA) or Paralel ATA PATA
     • Integrated Drive Electornics (IDE) aka ATA
       • only one device read/write at a time, master/slave config
   • Serial ATA (SATA)
     • reduced cable size lower cost native hot swapping faster throughput more efficient data transfer slower than SCSI
   • Small Computer System Interface (SCSI)
     • higher cost difficult config more noise and heat faster speed greater scalability
   • Serial attached SCSI (SAS)
     • to replace SCSI backward compatible with SATA lot faster and lot smaller than SATA mostly for servers
   • Fibre Channel
     • high speed network technology used in storage networking

3. Access speed

   • Seek time
   • Latency
   • RPM
     • 15000 RPM=2ms latency

4. SSD

   • DRAM or flash memory boards
     • majority NAND flash
   • memory bus board
   • CPU
   • battery (optional)
   • faster response time

5. USB drive

6. Tape

   • long-term storage
   • sequential access
   • off-site storage

7. Tiering

8. RAID

   • redundancy
   • RAID 1
     • mirror
   • RAID 0
     • stripes
     • never for production servers (data loss)
   • RAID 10
     • RAID 1+0
     • no parity
       • good for high write rate
   • RAID 5
     • min 3 drives
     • stripes
     • parity (XOR)
     • not for OS
       • parity calculation for data stays short time not worth RAID 5 page file is written all the time at OS
       • good for high read low write rate
   • RAID 6
     • two parity blocks
     • loss of two hard disks
     • min 4 drives
     • slower to RAID 5

9. File system types

   • Unix file system (UFS)
     • Unix
   • Extended File System (EXT)
     • Linux (EXT4)
   • File Allocation Table (FAT32)
     • max file 4 GB, max 2 TB
   • New Technology File System (NTFS)
     • encryption
     • max file 16 TB, max 256 TB
   • Virtual Machine File System (VMFS)
     • VMWare ESX, vSphere
     • Store virtual machine disk images
   • Z File System (ZFS)
     • Sun Microsystems
     • protection against data corruption
     • high storage capacities
     • encryption
     • 128 bit