[X Servers] XServe RAID 1 (mirroring)

[Peter Clarke]

>Greetings,
>
>I'm considering getting an XServe that would be installed at a 
>co-location facility.
>
>Since I don't have (easy/quick) physical access to the machine, I'm 
>considering getting a two drive XServe and setting up RAID 1 
>(mirroring) for data redundancy.
>
>(a) Is this supported by the RAID software bundled in OS X Server? 
>Or do I need third-party drivers?

	Both Raid 0 and Raid 1 are supported.
	Raid 1 is what you want in this case.


>(b) Will this automatically handle a drive failure and fail-over to 
>the working drive until a replacement is installed?  Will the RAID 
>software automatically mirror a replacement drive from the working 
>drive?

	Yes, if one drive fails, the other mirrored drive will continue
	to provide a service.


>(c) Can the XServe boot from a RAID 1 drive?

	Yes.  Earlier G4's could not do this, but the XServe can.

Extra Notes:

	I haven't got an XServe! - but we were thinking about buying one
	and so I looked into all this.

	- But it was decided to use our new Novell servers instead.

IMPORTANT:

	Say that you set it up with raid 1 (two disks).
	Then a disk fails
	- The service continues from the other disk.
	(but now without redundancy...)

Here is an interesting scenario:
	You want to replace the faulty disk and re-raid.
	The server has to be taken off-line,
	The replacement disk fitted.

	The server booted from ANOTHER disk
	(either firewire or CD)  (During the re-raiding process)
	- You can't run off the second disk 'during re-raiding'

	The new disk formatted, re-raided
	- that sync process could take some time - up to two hours

	Then the server is usable again.  (not usable while re-raiding).

	An alternative to this, for greater 'uptime'
	is to add another disk 3rd disk, also with a system on,
	synchronized with 'psync' say at midnight say.

	then if you need to re-raid, you could boot from this third disk, and
	still provide a service while the raid is being rebuilt
	Then, resync back to the raid, then reboot from the raid and 
continue as
	before.

	Because this is all built in, it's more convenient
	And it could (I think) all be done from off site
	- with the exception of fitting the new drive of course.

As you know, the Xserve supports four disks, so other combinations 
are also possible.  But greater redundancy come at greater cost.
- So you have to decide what is important to you,
saving £ (or $) or reducing downtime.

I was considering using an XServe, and an XRAID.

But instead we will use a Novell server and a SAN system.
- Except that we haven't got it working with Macs yet...



>Finally, has anyone had any problems with drives on an XServe?  Am I 
>just being paranoid?  Could I get away with just one drive, a good 
>backup strategy, and saying my prayers every night?
>

-- 
Peter Clarke, Harrow Campus Computing Services,  Technical Support. (Projects)
Ext 4685; Room L1.07; Learning Resource Centre.