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From Ulul <had...@ulul.org>
Subject Re: Hadoop and RAID 5
Date Tue, 07 Oct 2014 20:38:25 GMT
Yes, I also read in P420 user guide that it was RAID only. We'll live 
with it I guess...
Thanks for the HP/Cloudera link, it's precious reading !

Le 07/10/2014 08:52, Travis a écrit :
>
>
> On Sun, Oct 5, 2014 at 4:17 PM, Ulul <hadoop@ulul.org 
> <mailto:hadoop@ulul.org>> wrote:
>
>     Hi Travis
>
>     Thank you for your detailed answer and for honoring my question
>     with a blog entry :-)
>
>
> No problem.  I had been meaning to write something up. Thanks for the 
> prod. :-)
>
>
>     I will look into bus quiescing with admins but I'm under the
>     impression that nothing special is done, the HW RAID controller
>     taking care of everything, HP doc stating that inserting a
>     hot-pluggable disk induces one or two seconds pause in disk
>     activity. I'll check whether this is handled through the
>     controller cache and/or done out of business hours for safety.
>
>     I'll ask for internal benchmarking hoping it will convince
>     everyone to accept the JBOD model and automate what's necessary
>     for it not to disrupt operations
>
>
> Make sure your HP disk controllers can actually do JBOD.  Last I 
> looked (admittedly, this was ~3 years ago), you could only simulate it 
> doing multiple single-disk RAID0 LUNs. Operationally, these were one 
> level annoying more than just JBOD because now you had to 
> remove/destroy the RAID0 LUN when replacing the disk before you could 
> recreate the filesystem.
>
> At the very least, HP's reference architecture for Cloudera Hadoop 
> 5.X, updated in August 2014, shows that this is still the case.
>
> From their document:
>
>          Drives should use a Just a Bunch of Disks 
>
>         (JBOD) configuration, which can be achieved with the HP Smart
>         Array P420i controller by configuring each individual disk as 
>
>         a separate RAID 0 volume. Additionally array acceleration
>         features on the P420i should be turned off for the RAID 0 data 
>
>         volumes. The first two positions on the drive cage allow the
>         OS drive to be placed in RAID1. 
>
>
> http://h20195.www2.hp.com/V2/GetDocument.aspx?docname=4AA5-3257ENW&cc=us&lc=en
>
> If you've already got equipment, then probably not a big deal.  If 
> you're in the process of evaluating new stuff, I'd ask your HP 
> Var/Reseller if there was a different, non-RAID option, especially if 
> they have something similar to the LSI-9207-8i card which uses the 
> LSI2308 SAS chip.  I know Dell validated this with their 12G equipment 
> for use with Hadoop earlier this year.  Definitely a great card so far.
>
> Travis
> -- 
> Travis Campbell
> travis@ghostar.org <mailto:travis@ghostar.org>


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