Memo on RAID

What is RAID? RAID, abbreviation for redundant array of independent disks, is a technology to manage disk IO in multiple disks. (more accurate and detail version of definition is at Wiki (

RAID has few different types and called RAID 0, 1, 2, 3, 4, 5, 6.

It’s not like I did background check on facts, but I hear, the most popular types are RAID 0 and 5 today.

RAID 0 evenly distribute data across n number disks.  It’s simple straightforward way to take advantage of adding multiple disks.  The risk, if one of the disk goes wrong, then it’s all gone.

RAID 5 distribute data across n number disks randomly, plus parity information on one of the disk, so if one of the disk is damaged, you can recover like nothing happened.

Next I will organize pros, cons, and theological speed of each RAID.

Note on HTTP/2

This is me taking note on HTTP/2.

What is the problem with HTTP/1.1 ?

Modern websites requires lots of resources.  And resources are communicated through TCP, and TCP is slow in starting, because it required key value exchanges, three way hands shaking etc.  And we call that RTT (Round Trip Time).

Some uses KeepAlive flag to keep single connection and use this single connection with multiple resources.  But this also have problem, because when one resource takes up time, all resources behind the line gets stuck.

With TCP/1.1, it made it possible to have 6 instances of resources to be handled at same time.

What people try to do within limitation of HTTP/1.1.

6 is better than 1 but demand for resources to travel over http exceed 6 times more, so people had to come up with ways to reduce request over http.

Continue reading “Note on HTTP/2”