RAID question

[groovin]

i dont know too much about RAID mirroring. im looking at server specs and am wondering how many HDs i should get. i know with RAID, ill need at least 2. now suppose i only get 2 HDs. can i make 2 partitions on the first HD, one for the OS installation and other to hold shared files, and have the second HD RAID the both of them or can i only mirror a single partition on the HD?

if i mirror the system drive (were the OS is installed) and the drive fails, does the raid drive automatically take control or does the system die until reboot?

 

[bozo1]

With anything besides RAID-0 (which is not really RAID), you mirror entire disks, not just the partitions. If one drive dies, your server stays up - the system doesn't die. If you are running RAID on hot-swapple SCSI drives, and the Raid controller you buy supports it, you can even replace the failed drive and it will automatically rebuild - no downtime at all.
With IDE Raid you'll need to bring the system down to replace the failed drive.

Your system sees Raid array as one disk.

 

[groovin]

so, supposing im using IDE RAID and the disk dies and the server stays up as you said... all i would need to do is take the server offline and install a new disk to replace the dead one and the RAID will automatically (well, maybe not completely automatically) rebuild the new HD? Would I need to manually restore the partitions or would the RAID just completey copy itself to that disk?

thanks

 

[DoDau]

A good RAID Controller will automatically rebuild the array upon detection of the newly inserted drive.

The partitioning and formatting of drive space occurs after the array has been defined. Once the array is defined the system hands over 1 (if you have only defined one array) logical drive to the administrator for his use. From there you can create primary and extended partitions completely oblivious to the fact you have seperate physical drives in the system.

But it all comes down to the Controller and its Firmware abilities. Even a top of the line IDE raid controller can do hotswapping if needed. But these types of controller cost $$$$. and SCSI RAID controllers have had this ability for a long time.

Good Luck!

-DoD

 

[groovin]

is RAID fairly transparent to the OS?

 

[Saltin]

Is RAID fairly transparent to the OS?

Hardware Raid is completely transparent to the OS (short of it needing the right drivers and resources for the RAID card)

 

[Fuzznuts]

yes hardware raid is controlled by the cards themselves the OS obvisouly needs drivers to see the cards but the OS will only see drives how the are confgigured ie raid 1,0 or 0+1 will be irrelevant to the os.

Damm beaten to it

 

[groovin]

can anyone recommend a RAID card compatible with windows and linux? i have a dual boot going.

 

[DoDau]

Adaptec pretty much lead the chip-based (hardware) RAID market. Their Add-on card solution (SATA RAID0 and 1) 1210SA Supports Suse and Redhat Distro's and is a fairly cheap card.

Further up the food chain is the Adaptec ATA 2400A which is a 4 channel (4 IDE ports) RAID 0, 1 and 5 solution. A Lot more expensive, but is i960 chip based (all the RAID processing is done on the card, rather than the CPU lending a hand to the processing as is done on intergrated RAID controllers on current motherboards). This card supports older versions of Suse and Redhat.

Being the open source world that is Linux you might find some drivers for other distro's out there not made the manufacturers of raid cards/chips.

To implement RAID your going to have to blow away any current drives you have if you wish to add them to an array. You cant (yet) migrate a single drive system transperantly into a RAID array without a rebuild. Intel's SATA raid controllers on their latest mobo's can do that i think or will be able to shortly.

If you want to Dual-boot after creating an array it would be best to start with the WinXP install first. Pressing F6 during the first few seconds of the first install disk will tell the installer you wish to install the RAID drivers for the raid controller prior to installing the OS. After that, then go for the Linux install. Should work fine.

Although i'm not speaking from experience, if this is not the case someone post a reply and let Groovin know an alternative procedure.

Good luck.

 

[groovin]

"To implement RAID your going to have to blow away any current drives you have if you wish to add them to an array. You cant (yet) migrate a single drive system transperantly into a RAID array without a rebuild. Intel's SATA raid controllers on their latest mobo's can do that i think or will be able to shortly."

what do you mean by blow away? so, i wouldnt be able to take a single HD linux machine, throw in a RAID card and second HD, define the array, and have the RAID card automatically mirror the two drives (that is, populate the second drive with data)?

 

[DoDau]

Ahh,

Mirroring might work. I've never created a mirrored array with an exsisting drive. But, as i said before, it all depends on the capabilities of the RAID controller.

Unless some one else knows for sure and posts something here I'd say give it a shot. It should tell you if its possible or not before you define the array anyway.

 

[Nothinman]

what do you mean by blow away? so, i wouldnt be able to take a single HD linux machine, throw in a RAID card and second HD, define the array, and have the RAID card automatically mirror the two drives (that is, populate the second drive with data)?

I doubt you'll be able to do that, when the array is created metadata is written to all the drives involved which generally goes where the boot record and partition table of the single drive would go so everything gets erased. If you do find a card that allows you to migrate a drive into a mirror I'm sure it'll be realy expensive.

 

[groovin]

i see, i guess ill give it a shot anyways... just to see whatll happen. thanks

 

[skyking]

Arrays are neat, but like he said above, the way they create themselves and deal with the boot sector is unique. You have to build them up from scratch, but once you have them going, the possibilities are nice.
I have one going with some WD 20 gigs, and I can drop in a third drive and have it build it as a backup anytime. Don't have to wait for a drive to fail.

 

[DoDau]

That would be a 0, then a +1. A very good way of getting speed with redundancy without forking out several cartons of australium premium beer's worth of dosh.

As i said in an earlier post, Intels new 875/865 chipsets will have SATA raid controllers built into the ICP (on some models) which do allow the building of drive arrays. I dont think this will be 'hot' building as can be done in server SCSI RAID controllers, but it will retain your partitons and information.

I am about to purchase a Clearwater Server board with ATA RAID functionality and plan on doing a little experimentation with it before i finally build it up to the high end workstation it is going to become.

I'll post my results for you guys to see.

 

[groovin]

>>I'll post my results for you guys to see.

thatd be great!