What is Mirroring, Hotswap, RAID mean?

[nutjugger]

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Im new to these technologies. I just want to know the basics with illustration or examples.

What is Mirroring, Hotswap, RAID mean?


Thanks.

[EarlZ]

Mirroring;
Or so called RAID1 , basically this is a real time back-up of a selected hard drive using ( preferably ) the exact same drive model/speed/size
it is usually used on server type computers they use RAID0 config, ( RAID0+1 ) so if any one of the RAID0 array faiils your data is still safely stored on the mirrored drive.

Hotswap;

Same technology used in USB drivers and eSATAII and SATAII ports basically it allows removal of the drive at anytime or thru a software command to eject the drive.

RAID; ( kani gi copy paste rani nako )
rād) Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.
There are number of different RAID levels:

Level 0 -- Striped Disk Array without Fault Tolerance: Provides data striping (spreading out blocks of each file across multiple disk drives) but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost.
Level 1 -- Mirroring and Duplexing: Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks.
Level 2 -- Error-Correcting Coding: Not a typical implementation and rarely used, Level 2 stripes data at the bit level rather than the block level.
Level 3 -- Bit-Interleaved Parity: Provides byte-level striping with a dedicated parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely used.
Level 4 -- Dedicated Parity Drive: A commonly used implementation of RAID, Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails, the parity data is used to create a replacement disk. A disadvantage to Level 4 is that the parity disk can create write bottlenecks.
Level 5 -- Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.
Level 6 -- Independent Data Disks with Double Parity: Provides block-level striping with parity data distributed across all disks.
Level 0+1 – A Mirror of Stripes: Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. Used for both replicating and sharing data among disks.
Level 10 – A Stripe of Mirrors: Not one of the original RAID levels, multiple RAID 1 mirrors are created, and a RAID 0 stripe is created over these.
Level 7: A trademark of Storage Computer Corporation that adds caching to Levels 3 or 4.
RAID S: EMC Corporation's proprietary striped parity RAID system used in its Symmetrix storage systems

[marcus_aurelius]

Nice info... For reference, UP!

[MelodyMan]

Hi,

I just wanna ask...If two HD are striped, can I access the files separately when either of the drive is taken out? Assuming all are just data files, no system files.
For instance, I remove the HD1 and attach it to another server(server B). Will I be able to read the HD1 files on server2? Since I took the HD1 out without breaking the stripe, I guess server A stripe will be lost when I boot server A again. If I attached HD1 to server A, will it automatically restore the stripe?

With raid Level 0+1, can I mirror the striped drives into one hard disk? Should the capacity of the hard disk which contains the striped data equals to to stripe size?



thanks a lot!

[EarlZ]

Hi,

I just wanna ask...If two HD are striped, can I access the files separately when either of the drive is taken out? Assuming all are just data files, no system files.
For instance, I remove the HD1 and attach it to another server(server B). Will I be able to read the HD1 files on server2? Since I took the HD1 out without breaking the stripe, I guess server A stripe will be lost when I boot server A again. If I attached HD1 to server A, will it automatically restore the stripe?

With raid Level 0+1, can I mirror the striped drives into one hard disk? Should the capacity of the hard disk which contains the striped data equals to to stripe size?



thanks a lot!

You need both stripes on the same computer for its files to be read.
Mirroring a stripe only requires 1 physical hard drive

[yob]

before you need a RAID card to do RAID...

now it is already native with SATA

[EarlZ]

before you need a RAID card to do RAID...

now it is already native with SATA

you needed a raid card before to run IDE drives in raid mode...
when sata was introduced RIAD was already a built-in feature

[MelodyMan]

thanks EarlZ.

>You need both stripes on the same computer for its files to be read.
So does this means that I cant read files in one of the striped drive even I go DOS mode or boot VIA CD-ROM using Windows installer CD or Knoppix? What will the system tell then if I try to access on of the striped drive?

Q2: With RAID 5, is it really necessary that all drives must have the same size & same speed(RPM)?
Q3: Would it be ok if I transfer my OS to IDE drive? This will be mirrored IDE. And the all data files are just on SCSI with RAID 1. Currently, I just have 4 SCSI drives which are Mirrored.

Sorry to ask so much questions. Thanks coz you've been a great help!

[EarlZ]

thanks EarlZ.

>You need both stripes on the same computer for its files to be read.
So does this means that I cant read files in one of the striped drive even I go DOS mode or boot VIA CD-ROM using Windows installer CD or Knoppix? What will the system tell then if I try to access on of the striped drive?

Q2: With RAID 5, is it really necessary that all drives must have the same size & same speed(RPM)?
Q3: Would it be ok if I transfer my OS to IDE drive? This will be mirrored IDE. And the all data files are just on SCSI with RAID 1. Currently, I just have 4 SCSI drives which are Mirrored.

Sorry to ask so much questions. Thanks coz you've been a great help!

Q1:

You'll prolly get an error message if a stripe is missing something like "Raid array missing/broken... bla bla bla fix bla bla bla" so you need both drives to complete the stripe since every single file is striped on both drives its like eating a pizza w/o the topings.

Q2:

Basically you need the exact same model of the hard drive to have it mirrored w/o any dataloss or much of a performance hit on your system, having a smaller mirrored drive would result on a incomplete mirror since it is smaller.

having a slower drive with the same capacity could work if your using a PCI raid card that uses DIMM modules,some raid controllers can load that information on the system memory while the slower but same capacity drive is writing the information

Q3:

Raid controllers can mirror a drive regardless of its native interface( SATA/PATA/SCSI )

"And the all data files are just on SCSI with RAID 1. Currently, I just have 4 SCSI drives which are Mirrored."

I dont quite understand this part, if your using 4 SCSI disks to mirror your RAID 1 array then that means your using a total of 4 arrays ( 8 SCSI disks and 4 more for mirroring ? )

[MelodyMan]

Q1:

You'll prolly get an error message if a stripe is missing something like "Raid array missing/broken... bla bla bla fix bla bla bla" so you need both drives to complete the stripe since every single file is striped on both drives its like eating a pizza w/o the topings.

Q2:

Basically you need the exact same model of the hard drive to have it mirrored w/o any dataloss or much of a performance hit on your system, having a smaller mirrored drive would result on a incomplete mirror since it is smaller.

having a slower drive with the same capacity could work if your using a PCI raid card that uses DIMM modules,some raid controllers can load that information on the system memory while the slower but same capacity drive is writing the information

Q3:

Raid controllers can mirror a drive regardless of its native interface( SATA/PATA/SCSI )

"And the all data files are just on SCSI with RAID 1. Currently, I just have 4 SCSI drives which are Mirrored."

I dont quite understand this part, if your using 4 SCSI disks to mirror your RAID 1 array then that means your using a total of 4 arrays ( 8 SCSI disks and 4 more for mirroring ? )

First of all, thanks for replying.

Q1:

Just to clarify. Would I be getting that I kind of message even if I attach that striped drive on another computer?

Q2:

RAID 5 is data striping at the byte level and not exactly mirroring. Does is it really have to be same brand & capacity? For instance, if I will setup a RAID 5 using four SCSI HDs, should all have the same brand and capacity? Poor me. Only two of my drives have the same brand and capacity.

Q3:

Sorry to confuse you but I was actually asking about performance. Right now I have four SCSI disks. SCSI 0 & 1 is mirrored. This is where the OS resides. SCSI 2 & 3 is striped. This is where the data files reside. SCSI 0 & 1(17GB) have the same size. SCSI 2 & 3 have the same size(34GB)...I was thinking of buying new PATA drives for my OS. So there would be IDE1 and IDE2, same size same speed. IDE1 will be mirrored to IDE2. I will format my SCSI 0 & SCSI 1 so that I can make them part of my data drive. I will make a RAID 5 of the four SCSI Hard Disk. My OS will be in IDE1. If IDE1 fails, I will use IDE2. I know PATA is a bit slower compared to SCSI. Would this be ok?

Thanks!