What are the different RAID options for SAS

jana used Ask the Experts™
I have a server Xeon cpu, 4gb ram and 2 150gb SAS on a RAID.

I would like to make an upgrade and would like to know what options are available for RAID setup (FYI: the manufacturer indicates max storage is 700gb).

What different type of RAID for SAS and which would be the optimum option?
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Markus VordererOwn Company
It depends on what you will do with the server.
how many HDU's can you bring in the Server?
If 2 only Raid 0 (Striped) or Raid 1 (Mirrored) are possible
If 3 an more Raid 0 no Hotspare , Raid 1 with Hotspare or Raid 5 no Hotspare are possible
For Raid 10 you need at least 4 HDU's and more if you plan to give the Raid a Hotspare.

Perfomance an Risk of Data Loss:

Raid 0 good Read/Write Performance but Data Loss if 1 HDU Fails
Raid 1 good Read and Medium Write Performance no Data Loss if 1 HDU Fails
Raid 5 Medium Read/Write Performance no Data Loss if 1 HDU Fails
Raid 10 good Read/Write Performance no Data Loss if 1 HDU Fails

Best Regards

You have only 2 HDD so you can use mirrored (RAID 1) or Striping (RAID 0) options.

If you can get more HDD then you can go for RAID 5 and it is the best option if you have 3 or more HDD.



I think is only two.

Can you describe in less tech terms the difference in raid 0 (stripping) and raid 1 so I can talk to my boos (he is not a tech)

Raid 1 would be your best bet for better recovery and performance.
Own Company
When you build a Raid 0 with 2 Disks with 150 GB. The disks are striped together an you get a cap of 300 GB. The Date will be placed on the stripe.
When you build a Raid 1 with 2 Disks with 150 GB. The  Disks are configured that on each Disk go the same data on it. Tha cap is 150 GB.

Top Expert 2010
RAID1 means each disk has same data.  As bad blocks are created by the disks (it is inevitable), then data is automatically repaired by the controller by reading the same block from other disk.  RAID0 is (simplistically) concatenation.   RAID1 also protects against a drive failure.   RAID0 means, lose one disk, lose 100%.   For sake of argument, if each disk is 1GB in size, then RAID1 gives 1GB total usable.  RAID0 gives 2 x 1GB total usable.

Just buy RAID1.  You have to be nuts to buy RAID0 for a server, as there is no protection against partial or full data loss.
It all depends what you want to do with the server.

99% of the time you would choose Raid 1, which mirrors the same data onto both disks (giving a 150gb drive) allowing for failure of 1 of the disks and the server will keep running - as the data was on both.

the other 1% would be if you do not care if the disk dies and you lose everything and just need fast access to the disks (data number crunching). In this case you would want raid 0, which creates a single 300gb drive, and the data is split across both disks for quicker read/write times.

The the price of extra drives these days, there is little reason not to go RAID 1, unless speed is your only concern.

Getting more drives will open up more options, but all will have some form of redundancy to allow for disk failure in the server.


Thanx all great info!

What is "with Hotspare" or "no Hotspare" ?
Markus VordererOwn Company
Hotspare is a Disk which will go active if one Disk fails
@ Ramante.

For your case you have only 2 drives so you need to get another extra hard disk to have it has a hot spare.

If you create RAID 0 then you do not really require hot spare as data is going to write on both hard disk. If one hard disk fails then you will loss data.

RAID 1: you need to have two hard disk to use RAID 1 (mirrored) it keeps same data on both disk. For example you have 150 GB of two hard disk and you have created RAID 1 then you will be able to use only 150GB even though you have 300GB available. You can have another Hard disk and configure as hot spare so that when one hard disk dies it uses hot spare hard disk.

RAID1: you will not loss data if one hard disk fails.

If you can not have more than 2 Hard disk then go for RAID1 (Mirrored) best option for you in case you loss one hard disk still you will not loss any data.


Thanx all



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