Module 5: Block, File & Object Based Storage Systems (Block Based Storage)

Question 1

What is a block based storage system?

Answer 1

data stored on disks in blocks containing fixed number of bytes

Question 2

How big is a data block typically?

Answer 2

512 or 4096 bytes

Question 3

What do block based storage systems do?

Answer 3

store raw data only
maintain the file system software
can either scale up or out

Question 4

What does a file system do in a block based storage system?

Answer 4

adds an organization structure to the block data in OS

Question 5

What are the front end ports in a block based storage system?

Answer 5

connect hosts directly to storage system - hosts only connect through front end ports

Question 6

What access do the front end ports have?

Answer 6

only to the hosts they’re connected to - no direct access to any other devices

Question 7

What are front end ports connected to?

Answer 7

front end controllers

Question 8

What is the function of front end ports to the hosts?

Answer 8

provides connectivity protocol logic like FC or iSCSI and for mainframe host protocols ESCON and FICON

Question 9

What type of cache is in block based storage systems?

Answer 9

high speed DRAM memory

Question 10

What does the cache do in a block-based storage system?

Answer 10

buffers inbound data before writing to disk and buffers outbound data before going to host

Question 11

What increases IO performance in block based storage systems?

Answer 11

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

Question 12

What are the back end ports in a block based storage system?

Answer 12

connect through link control cards to shelves of physical disks and devices in each disk array enclosure (DAE)

Question 13

What is the disk array in a block based storage system?

Answer 13

contains the drives - only accessible by controllers

provides physical block storage capacity to storage system

Question 14

What does adding DAEs in a block based storage system do?

Answer 14

increase capacity and IO performance

Question 15

What is a storage controller?

Answer 15

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

Question 16

How is cache used to increase host read IO performance?

Answer 16

host sends read request to front end port

if requested data is in cache it quickly sends it back

Question 17

What is it called when a host requests data that is sitting in cache?

Answer 17

Read Hit

Question 18

What happens in a read scenario if the requested data isn’t in cache?

Answer 18

request is forwarded to back end ports and link controller to disk

Question 19

What is it called when a host requests data that is not sitting in cache?

Answer 19

Read Miss

Question 20

How is a cache write-back operation conducted?

Answer 20

written cache data eventually needs to be dumped to disk

typically written to host during low host activity

Question 21

Why can writing from cache to disk be done later in the day?

Answer 21

no impact to IO performance writing from cache to disk

Question 22

How is a cache write-through operation conducted?

Answer 22

data written to cache immediately sent to disk - acknowledgement is sent from disk to host once data arrives

Question 23

What is the benefit of a cache write-through operation?

Answer 23

since data immediately goes to the disks from cache the risk of data loss is low

Question 24

What is a con of a cache write through operation?

Answer 24

write response time longer since bypassing cache speed by writing straight to disk

Question 25

What is the Fibre Channel protocol?

Answer 25

high speed block data transfer

guarantees in-order delivery of block data from disk - drives designed for high performance

Question 26

What is SAS protocol?

Answer 26

Serial Attached SCSI - designed for midrange block IO

good balance of storage and performance

Question 27

What is SATA protocol?

Answer 27

Serial Advanced Technology Attachment - used in less demanding block workloads

high capacity

Question 28

What is NVMe protocol?

Answer 28

Nonvolatile Memory express - provides highest block IO transfer and lowest latency