On Thu, 5 Apr 2001, Federico Sevilla III wrote:
..
> This brings me to my question: RAID 10 or RAID 5? I haven't found anything
> comparing the two as far as performance is concerned. Here's a little
> kuwento about the two RAID levels for those who don't know, though. It can
> also help in figuring out where I'm coming from (why I'm trying to decide
> between the two).
Quick answer: it depends.
RAID5 distributes the parity across the drives, HOWEVER it still needs to
write the parity bit for EVERY write. Therefore: RAID5 is no faster than a
single drive on writes (bottlenecked by the parity-write requirement). On
reads, it's pretty fast (data is striped over the drives in the array).
RAID1 is the ultimate in redundancy. But it's no faster than a single
drive either, because the bits have to be written to all drives. In fact,
it can be slower if the drives are not "spindle locked" e.g. rotating at
the same speed. Read performance sucks too (single-drive speed), no
benefit alternating spindles because they all hold the same information
anyway.
RAID0 is faster than RAID5 on reads (striping over all N drives, rather
than N-1) and much, much faster on writes (striping over all drives, no
parity write bottleneck). But most prone to failure (worse than single
drive!)
SO:
- if you want sheer speed and damn the torpedoes: RAID0
- if you want maximum redundancy and damn the cost: RAID1 (2N drives
required): you can survive the loss of 2N-1 drives!!
- if you want maximum value for money and some redundancy: RAID5 (N+1
drives required): you can survive the loss of 1 drive
- if you want maximum speed AND redundancy: RAID1+0.
with four disks, I would go RAID5. A RAID1+0 configuration in such a case
would only give you SIZE x 2 storage, RAID5 will give you SIZE x 3. If you
really need the speed and need RAID1+0 though you need more drives. A
RAID1+0 configuration with less than 8 drives is iffy.
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