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RAID 5

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by arief

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We are going to have a server install. This is my frist w2k server. It would be use for file sharing and also small data base. I would like to have RAID5. The server would have 3 SCSI (36.4GB)HD. I was woundering if I need to have additaion smaller HD,just for system and boot partion. So i can use the other 3 HD for RAID 5 with no waste of HD.

10 replies

by jellimonsta

You could have a seperate drive for OS but if you are to do so I would personally recommend using a seperate RAID backplane and having the drive mirrored. RAID 5 is used because of its redunancy capabilities but if you have the OS itself on a seperate drive you still have a single point of failure for the server. I am sure other Admins would have other suggestions though.

by omie

This is a good question but in my own experience I am using two EIDE hard drive and that is where I put the OS and the data will be on Raid 5.In terms of speed and data speed I don't see much difference. EIDE drives run neck to neck with the SCSI drives in terms of data acces and besides it cost less.It is also easier to configure for you don't need to put scsi ID (master and slave). The only thing you need is to set up those drives in mirror.

Any comment using EIDE drive for OS ? Does anybody experienced a problem using eide drive mixed with the SCSI ? Please share....
Thanks

by ghstinshll

IDE RAID is slower than SCSI raid, especially when I'm assuming your solution is a software RAID. SCSI drives have better throughput, period. Newer IDE, SATA drives will be as fast as the current SCSI, adn RAIDable as easily as well...

No need for the 2nd drive, unless this system will need it. Is the current database running on a slower server? If so, the upgrade alone will afford you just one RAID 5 array, including the OS. Unless this is a multi CPU server, with millions of transactions to be done, there shouldn't be a need to put the OS on another array or mirror.

by omie

You didn't get my point...Using a separate drive for OS save you a lot of time in system restoration...(if your system crashes). If you need to rebuilt your server due to various reason you don't need to restore data from a backup for your data, foryou will be just doing the drives where you installed your OS. In raid you need to restore data if you need to re-install the OS.
Remeber you need the OS for services but not for data access so the performance is not affected.

by paulo540

For the system drive set (aka container) I would place my OS in a mirrored drive set using either an ATA raid card(inexpensive), or separate SCSI raid container. Then I would build the RAID 5 set for my data. The value added is separation between I/O. The system would be redundant and independent from the data storage set providing maximum uptime.

by lordinfidel

I always like to follow certain rules when building my servers.

The boot partition is always a mirrored set.
(usually 2 9's)

The data set, on a seperate controller as raid 5.

Now that's not to say that rules can't be broken.
If physical space (room to put drives) is an issue. Then opt for the filling it with drives and use raid 5.

Let's say you have a server with 4 drive bays. It would be better to put all 4 drives into a raid5 set then it would be to mirror 2 drives and leave the other 2 dangling.
When you boot into the OS set up menu, it will appear as one large drive. Simply partition the set into your boot and data partitions.

by nickhews

I've followed your comments with interest, but isn't there a potential problem with W2K server when you put the boot/system partition on a RAID5 set? I seem to remember that a system partition needs to be on a mirror set, especially for recovery purposes. Perhaps with everything on a 4-disk RAID 5 set you shouldn't get a failure!
Any comments?

by lordinfidel

And granted I am talking out my ass on this part because I don't believe in it nor have I tried it,

And that is software raid. I can see the potential problems using software raid5 and putting the boot partition on it. Especially using winblows.

But with hardware raid5;
(which I am a huge propenent of, basically if the data means that much that you would consider raid, don't dick around. Do it right the first time, use a hardware based raid system)
the OS does not care. It sees it asjust one big drive that you can partition the crap out of.

Same is true for a hardwarde raid1.

Let's say you mirror 2 72 gig bad boy's at the hardware level. The OS will only see it as 1 72 gig drive. You can create 7 10 gig partitions and 12 gig partition and ALL of the partitions will be mirrored.

However, when you install 2K or Nt4, you need to press the F6 key as soon as the installer begins to start. You need to specify your controller that it will be booting off of.

But even before then, you need to create your raid set from the controllers bios menu.

Each controller is different, but if you read the text on the screen as the system boots, it will say which card it is up to and to press some key combo to manage it.

by leehellcat

I agree with LordInfidel on this one. When setting up W2K servers I tend to use 2 x 9 or 18Gb drives mirrored for the OS partition. Then for my File Servers/DataBase Server, have 3 x 36Gb drives in Raid 5.

This way you have maximum Redundancy, and a few hundred bucks spent in the beginning can save a lot of downtime and expense at a later date.

by jellimonsta

The whole reason for having RAID 5 is so you can replace a drive if one goes bad (Reduncancy). In that case, if you do need to reinstall the OS you simply format that logical drive and reinstall the OS. Why anyone would want to install a seperate IDE drive is beyond me really.

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