On Mon, Jun 13, 2005 at 09:15:39AM +0200, Laurent CARON wrote: > Dan Stromberg a ?crit : > >>>Has anyone constructed a RAID 5 of RAID 5's using mdadm on a linux > >>>system? > >>> > >>>Was it reliable? > >>> > >>>How large was it? > > > RAID 10 is IMHO a bit more efficient. > > Raid 5 means at least 9 disks: > Usable capacity: 4 Disks > Read speed: Good > Write speed: poor With a low number of disks, you would indeed get the same or less capacity with RAID 5 + RAID 5 as compared to RAID 10, but as the number of disks gets higher, doesn't the capacity of RAID 5 on top of RAID 5 (we need a name for this, is RAID 55 technically correct?) get better? For example, 30 disks, organised as 10 3-disk RAID 5s, have 9*2 or 18 disks of capacity, whereas a RAID 10 of same would be 15 disks. The write performance seems bad though, and maybe the rebuild time as well.
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