RAID 5: Striping with Parity...

[Electric Amish]

Can you set this up on drives that already contain data, or does it have to be established from blank drives??

amish

 

[Boonesmi]

i could be wrong, but i belive you need to start with fresh drives

 

[Electric Amish]

So, I guess that means you cannot stripe the OS??

amish

 

[Vegito]

RAID controller need to establish RAID prior to installing software... so if you have unestablished drives... u would ghost ur current parition into a file, drop in 3 drives or more for your raid, create your paritions and restore ur ghost file into the partition and thats it..

 

[Shooters]

Yes, you can stripe the OS. In fact, if you're running a RAID 0 or RAID 5 then you have no other choice. As others have mentioned you have to set up the array before any data is written to the drives and then load the data onto the array.

 

[mikefromwa]

make a ghost of your current drive, setup the raid array and ghost it back ontop of it

 

[DaddyG]

AMISH obviously doesn't trust Electricity !!.

RAID level 5 can infact be used for the Operating System but it makes NO SENSE to use it. Its the OPerating System that is the "Other END" of the Partnership !!

If the SH!T Hits the FAN, WHO CLEANS off THE SH!T and RESTARTS the FAN !!

The BOSS aka the Operating Sytem !!

G

NO BOSS !!

 

[Vegito]

Hey Shooters.. maybe you know this.

I have 3 Atlas 10K RAID 5 right now. I need to increase the capacity of the RAID, its 18GB each = 54 total - 18 parity = 36 Available.

I think I gotta ghost out and add drive and put back in but do you think there is a way to add the drive on the fly and have the raid establish it self to the new drive ?

I doubt it but maybe there is a way... adaptec raid cards..

 

[Woodie]

You are talking about hardware raid right?(not the OS), if so it depends on the RAID controller.
Compaq RAID controllers: Complete data loss. Cannot extend a logical drive. Mylex DAC960*: Yes, you can "extend" a logical drive, without affecting the data. Adaptec: I don't have one, so don't know.

--Woodie

 

[Vegito]

yeah, got a nice adaptec 1130 with 64mb cache but manual didn't mention much... and dont have time to call tech support... haha

 

[JackBurton]

<< You are talking about hardware raid right?(not the OS), if so it depends on the RAID controller. >>


I was about to say that. The OS has no idea what is going on in hardware RAID. As far as it know, it is running off one single SCSI drive. Now if you are doing software RAID then yes, the OS is doing the work; HOWEVER, you can't stripe the OS in software RAID, that is if you're are using NT or 2000.

 

[shaoyeh0]

I'm hoping you guys can help me. I'm planning setting up raid 0 on my machine but I currently only have one drive. Can I use a similarly spec'ed hard drive as the second drive? I have a IBM 75gxp but I see a maxtor that is similarly spec'ed but much cheaper. Can I use the maxtor?

 

[JackBurton]

Yep, you won't have any problems. Just remember your RAID configure will only perform as fast as the slowest drive. Also if you have a 20GB drive and a 30GB drive, your MAX RAID 0 size will be 40GB (2 X 20GB). The other 10GB from the 30GB drive will be lost.

 

[Electric Amish]

Ok. Here's the full deal.

Our NT data server is running a mirror on 2 Seagate Cheetah 18gb drives. We are out of space, so we are going to add a third Seagate Cheetah 18gb and run RAID 5 (Stripe with parity). Can we do this without reinstalling the entire system??

The raid will be software (NT Server).

amish

 

[JackBurton]

This is what I'd do...Image your drive (since it is a mirror you really only have a drives worth of data) to another HD drive (one that is NOT going to be part of your RAID 5 config). FDISK to get rid of your partition on the two drives you were using as RAID 1(optional). Now setup your RAID card to do RAID 5 and FDISK again to create your partition (FDISK should be optional because when you put the image back, it should take care of the file system too). Now just move the image back to your newly created RAID 5 set up from the HD you had the image stored on. Should take about 20-30 mins.

 

[Electric Amish]

The RAID is being controlled by the OS not hardware.

amish

 

[JackBurton]

Ooooo, ya your going to have to do a reinstall.

 

[Pariah]

You are going to have to completely reconfigure your system Amish. RAID 1, which is what you are using, is the only NT controlled software RAID level that is bootable. RAID 5 is not bootable, so if you want a 3 drive RAID 5 array (a recommend against it), you will need a third drive for the array plus a new boot drive. Needless to say, this process will require a system wipe and a clean install.

 

[Electric Amish]

Why do you recommend against it??

Could I take 1gig or so and make that the boot partition then stripe 17gb on the 3 drives?

amish

 

[JackBurton]

Amish, is there a reason you are not doing RAID properly and use hardware to control your RAID array? Also, if you are going to do RAID in a business world RAID 5 is the ONLY way to go.

 

[Electric Amish]

We just don't have a RAID card.

The server is not hit that hard. Data that is generated in our labs is just automatically forwarded to the server and versioned. It is not accessed there by users, so speed isn't really an issue. It's really just a repository for the data until it can be archived to CD. The software RAID 1 has been working fine for awhile now.

amish

 

[Pariah]

RAID 5 in the wrong setup has really bad write performance. WinNT RAID 5 performance will write at about 5-7MB/s across the whole array, which is slower than typical FastEthernet throughput, as opposed to a single Cheetah drive which will write from 25-40MB/s. If write performance is not important, than a software RAID 5 array should work fine. Also, if the array gets corrupted it takes quite a while to rebuild the array. 12 hours+ is not unsual. I created a 4 drive array in Win2k, and the initial build of the array took 7 1/2 hours. RAID 5 can give you the best of both worlds, but in order to get the top notch performance that RAID 5 advertises you need a true hardware RAID 5 controller which does not come cheap.

 

[Woodie]

If this is for business, then absolutely, dump the software raid, and buy a RAID card, and do RAID 5. Software raid takes a very long time to recover, and doesn't take advantage of hot-pluggable hardware, etc...Is the point to have a lot of drive space? or to prevent data loss due to drive hardware failure? or to provide for minimum down-time?
Your goal makes a big difference as to which solution you choose. Rebuilding a 4gig drive in a hardware (Compaq) scsi raid5 setup takes us <30 minutes, with 0 downtime for the server. (no shutting down the box, reconfiguring the mirrored drive as the boot drive, turning off mirroring, and bringing the box back up. That doesn't include the time to replace the bad drive, and reconfigure.


/shameless plug-I have a Mylex (IBM) f/w 2 channel RAID controller for sale- /endshameless plug

My $.02 It's your money/time/effort that has to be spent, not mine.

--Woodie

 

[Hardware]

raid 5 is crap its slow like hell use raid 0 or raid 1 best raid 0+1