Different Type of I/Os generated by IO Tools

Block I/O:
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- Initiated through native device files /dev/sd*.
- I/O transfers in fixed-size blocks
- write I/O exchange consists of transferring data blocks from the address space of the calling process to the kernel’s buffer cache, and then to the disk device.
- a read I/O exchange consists of transferring data blocks from the disk device to the kernel’s buffer cache, and then to the address space of the calling process.
- type of I/O is primarily used to support file systems where frequently accessed data can remain resident in kernel buffers, eliminating the need to repeatedly access the disk device and where I/O can be queued in the buffers until a threshold is reached before a disk device transaction is performed, optimizing efficiency.

RAW I/O :
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- initiated through special raw device files.
- I/O transfers in fixed-sized blocks.
- bypasses the kernel’s buffer cache so data is exchanged directly to and from the address space of the calling process, reducing the amount of required system bandwidth and improving I/O throughput
- type of I/O is primarily used to support database operations where the size of transactions tends to be small and the performance throughput is more critical.

Scatter-Gather I/O or Character I/O:
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- initiated through special sg devices files /dev/sg* (or pass through driver).
-supports I/O of variable-sized blocks.
- provides direct access (i.e. pass-through) to SCSI devices, allowing the calling process to send direct SCSI commands to various devices including hard disks, CD-ROMs, and CD burners and to receive direct responses to the those commands.
- type of I/O is primarily used to perform low-level operations on SCSI devices that are not possible with the sd, st device drivers.

ASYNCHRONOUS I/O (or AIO):
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- initated through special raw device files /dev/raw* using the LIBAIO library
- supports I/O of fixed-size blocks.
- Once the calling process issues the I/O request and the request is queued to the destination device, it immediately regains control of execution, allowing it to issue additional subsequent requests. The completion of an I/O request can be signaled to the calling process or the calling process can periodically poll the status of its I/O request.
- type of I/O is primarily used for high speed applications such as computation-intensive processes

Host Based Migration Methods

Host-Based Backup and Restore Migration:(Disrutptive)

Here we use an utility to copy an existing disk/lun to a newly provisioned disk/lun. This requires additional storage of equal or greater size than the original lun. The migration will consume CPU cycles on the host.

The application will be offline for the copy duration and will be reconfigured once the copy is done.

1. Make the target LUN available to the host
2. Quiesce/stop the host application
3. Backup the source LUN to the target LUN
4. Reconfigure/Restart the application.

Host based LVM mirror:(Non-Disruptive)

This method also requires additional storage at least the size of the source LUN.There is no disruption to the application. But, host CPU cycles are consumed.

Steps

1. Make the target LUN available to the host
2. Add the target LUN as mirror to the LVM volume containing the source LUN.
3. Break the mirror after the destination is in sync.

Virtual Desktop Infrastructure

I was looking at getting into a peek at what is a Virtual Desktop infrastructure and its use cases / applications.

Have a look at these videos to get a preview of what it means

Part 1:

http://www.youtube.com/watch?v=zGDwD9afZ94&feature=PlayList&p=00122D416E40AD94&index=11

Part 2

http://www.youtube.com/watch?v=IRNR0KEOBQ4&feature=related