[GRLUG] RAID levels

[Richard Nienhuis]

Performance issues are going to be inconsequential for a machine playing
 music.  In degraded mode there is probably still enough performance.  Also
hot spare isn't going to spare you from the time to rebuild the array.

On Fri, Sep 30, 2011 at 4:59 PM, Mike Williams <knightperson at zuzax.com>wrote:

> Last night at The Warehouse we had a fairly involved discussion about the
> various RAID levels. I realized, while churning it over in my head again a
> little while ago, that one of my assumptions was not quite correct. I
> thought that in RAID 6, since you have an extra drive, that the system
> doesn't need to do parity reconstruction like RAID 5 does once you lose the
> first drive. Since even in RAID 6 there is actual data on that drive, it
> still has to do the reconstruction so you will still lose performance once
> the first drive failed. That being the case, would Casey's music box be
> better off in RAID 5 with a hot spare rather than RAID 6 without? RAID 6 has
> the advantage that the array wouldn't go down until the 3rd drive
> failure,while a RAID 5 array would go down on the 2nd. However, under RAID 5
> with a hot spare the rebuild of the array could start immediately, vastly
> reducing the time during which the array is running in degraded mode.
> Thoughts?
>
> For those who weren't part of the discussion, we have an array of 5 disks
> to RAID. RAID Level 0 is striping and isn't actually redundant: very fast, 5
> disks worth of storage, but a failure of any disk takes down the array (Bad
> Idea). RAID 1 is mirroring and uses half the available storage space. In the
> case of 5 disks, we would get 2 disks worth of storage plus have a hot
> spare. It would take either 2 or 3 drive failures before the rebuild
> finishes to take down that array. RAID 5 is like RAID 0 but with one drive's
> worth of redundancy. Any 2 drive failures will take down the array, it slows
> down significantly when the first one fails, and you get 4 drives' worth of
> storage. RAID 6 is similar, but can weather 2 failing drives but you only
> get 3 drives of storage (the same as RAID 5 with a hot spare). A "hot spare"
> is an extra drive that is installed and powered on but not used until a live
> drive fails, at which point it gets a copy of that drive's data and takes
> its place.
>
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