Big arrays from EMC and others typically allocate drives into raid groups. Over say 48 drives in a drive shelf you might configure 6 raid groups of 8 drives each. The array management software then allows chunks from all the raid groups to be striped into logical units that are presented to the host.<br>
<br>Remember that raid 5 uses a three block rolling parity scheme. The data on any single drive can be re-constructed from the two adjacent drives in the raid group. So the number of drives in the group does not impact the ability to reconstruct from a single drive failure.<br>
<br>If someone did create a raid 5 group with 1000 drives it it you would indeed get 999 drives worth of capacity. But other practical limits tend to get in the way of that big of a raid group deployment.<br><br><div class="gmail_quote">
On Wed, Apr 8, 2009 at 8:41 PM, Angelo Bertolli <span dir="ltr"><<a href="mailto:angelo.bertolli@gmail.com">angelo.bertolli@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
I know that things like RAID 5 need at least 3 disks, and can lose 1 disk. The biggest RAID sets I set up are RAID 6 with 12 disks, and honestly that's pushing it a bit for fault tolerance. But it does seem to work.<br>
<br>
Does anyone on the list know if there is an upper limit to the number of disks? I am sure there must be, as the parity can't possibly be rebuilt from just using one extra drive, if you have 1000 data drives, for example. I'm sure there has to be a tradeoff somewhere, like if I have 1000 drives, I'm not getting a capacity of 999 drives, maybe more like 900 drives.<br>
<br>
Angelo<br>
<br>
_______________________________________________<br>
clue-tech mailing list<br>
<a href="mailto:clue-tech@cluedenver.org" target="_blank">clue-tech@cluedenver.org</a><br>
<a href="http://www.cluedenver.org/mailman/listinfo/clue-tech" target="_blank">http://www.cluedenver.org/mailman/listinfo/clue-tech</a><br>
</blockquote></div><br>