On 16.12.2005 02:53, Neil Brown wrote:
On Thursday December 15, tobias.hofmann@xxxxxxxxxxxxxxxxxxxx wrote:
<delurk>
On 15.12.2005 21:46, Brad Campbell wrote:
Callahan, Tom wrote:
It is always wise to build in a spare however, that being said about all
raid levels. In your configuration, if a disk fails in your RAID5, your
array will go down. RAID5 is usually 3+ disks, with a mirror. So you
should
have 3 disks at minimum, and then a 4th as a spare.
/me wonders in the days of reliable RAID-6 why we use RAID-5 + spare?
Me too. ;) So, with holidays ahead, two questions (as I might tackle
that soon and have not found it mentioned):
- How would one "switch" from the latter to the former? Is there
something like "grow_to_RAID_6"?
No... at least not yet....
Hm. :) Around here, it is pretty much Christmas time, with all the
"wishing" going on - hint, hint? ;)
- Does RAID6 have disadvantages wrt write speed?
Probably. I haven't done any measurements myself, but from a
theoretical standpoint, you would expect raid6 to impose more CPU load
(though that may not be noticeable) and as raid6 need to see the whole
stripe to update the P and Q blocks (it cannot do a subtract old, add
new update) there could well be more IO happening, particularly on
large arrays (>5 devices).
That,s about the line of thinking I was considering. I,ll see, if I
tackle this over the holidays, to do some tests...
Of course, whether this caused noticeable reduction in throughput and
latency would be very workload-dependant.
My scenarios here @home will probably not be very relevant to what one
would like to know in a production environment - whatever that is... :)
Thanks for the input, Neil,
greets, tobi... :)
-
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
