Module 5: Block, File & Object Based Storage Systems (Block Based Storage) Flashcards
What is a block based storage system?
data stored on disks in blocks containing fixed number of bytes
How big is a data block typically?
512 or 4096 bytes
What do block based storage systems do?
store raw data only
maintain the file system software
can either scale up or out
What does a file system do in a block based storage system?
adds an organization structure to the block data in OS
What are the front end ports in a block based storage system?
connect hosts directly to storage system - hosts only connect through front end ports
What access do the front end ports have?
only to the hosts they’re connected to - no direct access to any other devices
What are front end ports connected to?
front end controllers
What is the function of front end ports to the hosts?
provides connectivity protocol logic like FC or iSCSI and for mainframe host protocols ESCON and FICON
What type of cache is in block based storage systems?
high speed DRAM memory
What does the cache do in a block-based storage system?
buffers inbound data before writing to disk and buffers outbound data before going to host
What increases IO performance in block based storage systems?
placing DRAM between disks and front end ports - in the path of the compute to disk transfer - means all IO must pass through cache first
What are the back end ports in a block based storage system?
connect through link control cards to shelves of physical disks and devices in each disk array enclosure (DAE)
What is the disk array in a block based storage system?
contains the drives - only accessible by controllers
provides physical block storage capacity to storage system
What does adding DAEs in a block based storage system do?
increase capacity and IO performance
What is a storage controller?
manages all the functions of the storage system
has the front end ports, back end ports
implement RAID and present LUNs to servers
manage the DRAM cache
also called RAID controllers
How is cache used to increase host read IO performance?
host sends read request to front end port
if requested data is in cache it quickly sends it back
What is it called when a host requests data that is sitting in cache?
Read Hit
What happens in a read scenario if the requested data isn’t in cache?
request is forwarded to back end ports and link controller to disk
What is it called when a host requests data that is not sitting in cache?
Read Miss
How is a cache write-back operation conducted?
written cache data eventually needs to be dumped to disk
typically written to host during low host activity
Why can writing from cache to disk be done later in the day?
no impact to IO performance writing from cache to disk
How is a cache write-through operation conducted?
data written to cache immediately sent to disk - acknowledgement is sent from disk to host once data arrives
What is the benefit of a cache write-through operation?
since data immediately goes to the disks from cache the risk of data loss is low
What is a con of a cache write through operation?
write response time longer since bypassing cache speed by writing straight to disk
What is the Fibre Channel protocol?
high speed block data transfer
guarantees in-order delivery of block data from disk - drives designed for high performance
What is SAS protocol?
Serial Attached SCSI - designed for midrange block IO
good balance of storage and performance
What is SATA protocol?
Serial Advanced Technology Attachment - used in less demanding block workloads
high capacity
What is NVMe protocol?
Nonvolatile Memory express - provides highest block IO transfer and lowest latency
