On 17/08/2012 00:11, vincent Ferrer wrote:
On Wed, Aug 15, 2012 at 10:58 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote:
On 8/15/2012 9:56 PM, vincent Ferrer wrote:
- My storage server has upto 8 cores running linux kernel 2.6.32.27.
- I created a raid5 device of 10 SSDs .
No it is not normal practice. I 'preach' against it regularly when I
see OPs doing it. It's quite insane.
There are a couple of sane things you can do today to address your problem:
Stan
Hi Stan,
Follow-up question for 2 types of setups i may have to prepare:
1) setup A has 80 SSDs. Question: Should I still create one
raid5 device or should I create 8 raid5 device each having 10 SSDs ?
My linux based storage server may be accessed by upto 10-20
physically different clients.
I have difficultly imagining the sort of workload that would justify 80
SSDs. Certainly you have to think about far more than just the disks or
the raid setup - you would be looking at massive network bandwidth,
multiple servers with large PCI express buses, etc. Probably you would
want dedicated SAN hardware of some sort. Otherwise you could get
pretty much the same performance and capacity using 10 hard disks (and
maybe a little extra ram to improve caching).
But as a general rule, you want to limit the number of disks (or
partitions) you have in a single raid5 to perhaps 6 devices. With too
many devices, you increase the probability that you will get a failure,
and then a second failure during a rebuild. You can use raid6 for extra
protection - but that also (currently) suffers from the single-thread
bottleneck.
Remember also that raid5 (or raid6) requires a RMW for updates larger
than a single block but smaller than a full stripe - that means it needs
to read from every disk in the array before it can write. The wider the
array, the bigger effect this is.
2) Setup B has only 12 SSDs. Question: Is it more practical to
have only one raid5 device, even though I may have 4-5 physically
different clients or create 2 raid5 devices each having 6 SSDs.
Again, I would put only 6 disks in a raid5.
Reason I am asking because I have seen enterprise storage arrays from
EMC/IBM where new raid5 device is created on demand and (storage
firmware may spread across automatically across all the available
drives/spindles or can be intelligently selected by storage admin by
analyzing workload to avoid hot-spots)
Partitioning was only done because I am still waiting budget approval
to buy SSDs.
regards
vincy
--
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
--
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
