My notes when reading from “Michael Doyle” book –
Thanks Michael for writing such a nice book.
Below are some points which I want to remember always J . Plan is to write such point from each chapter. I hope it will help others.
Recovery time Objective - > uptime of server.
· 99.9% -> 8.76 hours in year
· 99.99% -> 53 minute in year
· 99.999%-> 6minute in year
Recovery Point Object- > calculation of RPO depends on-
· Amount of data lost
· Cost to the company of lost data
· Cost to the company for the time to recover data.
SQL server mirror - > As per TechNet this feature is going to be removed from future version , plan to use “AlwaysOn Availability group “.Mirroring is implemented on a per-database basis and works only with databases that use the full recovery model.
Database mirroring maintains two copies of a single database that must reside on different server instances of SQL Server Database Engine. Typically, these server instances reside on computers in different locations. Starting database mirroring on a database, initiates a relationship, known as a database mirroring session, between these server instances. Database mirroring involves redoing every insert, update, and delete operation that occurs on the principal database onto the mirror database as quickly as possible. Redoing is accomplished by sending a stream of active transaction log records to the mirror server, which applies log records to the mirror database, in sequence, as quickly as possible. Unlike replication, which works at the logical level, database mirroring works at the level of the physical log record. Beginning in SQL Server 2008, the principal server compresses the stream of transaction log records before sending it to the mirror server.
Sql Server Clustering : two or more SQl Server node that act as a single Sql server instance. A Sql server cluster contains –
· A network name for cluster instance.
· One or more IP address for cluster instance.
· A combination of one or more disk.
· At least one sql server with one SQL server Agent, Full text search service.
· Registry key for checkpoints across nodes and dlls for failover process.
AlwaysOn [SQL server 2012]: Database mirroring +
A database can use either “AlwaysOn” or Database mirroring, not both.
SQL server log Shipping : SQL Server Log shipping allows you to automatically send transaction log backups from a primary database on a primary server instance to one or more secondary databases on separate secondary server instances. Log Shipping can be combined with DB mirroring.
Log Shipping versus Database Mirroring –
1. Infinite number of receivers in case of log shipping.
2. Failover is always manual.
3. Failover duration is slow as compared to database mirroring.
4. Log shipping use both committed and uncommitted transactions, db mirroring just use committed transactions.
SAN [Storage Area Network]: set of disk and tape can be viewed as single entity. Accessed at file block level.
RAID Redundant Array of inexpensive Disk
RAID 0 : disk stripping as writes blocks of data across disks.
RAID 1: Disk Mirroring, requires two disk, every bit is written over two disks.
RAID 5: data stripping with parity. Data is written over 3 disks.
RAID 10: equivalent to RAID 0 +1. Two sets of disk each with RAID 0 configuration.