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First time using Xen, I come from a vmware world but would like to expose myself to some Xen technology. With that said, I have a spare server (Dual proc, 8G of RAM w/ 2 x 500G sata drives). Stupid thing doesn't have HW raid so I'm forced to use software based. With that said, is it worth using software? I've read that software-based RAID could be slow, and I'm fine with syncing my data elsewhere for backup purposes.

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up vote 1 down vote accepted

Sounds like your 'playing'/testing - software RAID will be fine for that, some here are more than happy to use in production too. Obviously if you're doing a lot of writes it'll be slower overall as it'll have to write everything twice but iirc reads are pretty comparable.

Either way just get on with learning and when you look to go into production then look at performance :)

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Came across another thread that says the dom0 can't sit on a RAID1? Is that true? – luckytaxi Jun 23 '11 at 14:22

It's perfectly fine to run a Xen system on software mirroring. With "slow" 7200rpm SATA disks, I doubt you will incur in any noticeable performance hit when comparing to the same disks on an hardware controller (without cache, otherwise we would be comparing apples to oranges). Modern systems have enough I/O capacity to cope with 2x the traffic of a single slow _SATA disk.

Dom0 is nothing different from a standard linux system so yes, you can run it from software raid, using linux md driver autodetection feature.

What you cannot do is actually run the bootloader (grub) from a "software raid", but when talking RAID1 it's perfectly fine to put /boot on software raid1 and point GRUB to one of the two disks. It will be actually accessing a single disk and not a raid device, so things could get funny if you loose the first disk (the one where you usually boot from). If the disk does actually disappear from the system and if grub is installed on the second disk MBR too it could boot from the second disk, but if the first disk is still "visible" to the system while being b0rked / unresponsive grub could get stuck while trying to access it.

But, as already said, for a play/test environment it'll work like a charm.

PS, as an example I used to run a test server with 4 sata disks. dom0 was stored on a quad mirror (a partition mirrored on all 4 disks) and all the remaining space was striped in RAID0 for storing domU images (on logical volumes, from a single volume group composed of a single physical volume composed of the software raid0 composed of 1 partition from each disk).

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