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тАО06-19-2002 12:14 AM
тАО06-19-2002 12:14 AM
The above question needs a bit of an explaination. We will be soon moving over to VA7400 as a replacement to a 30 disk fc60 array. The basic unformatted disks seem to be similar in size 18, 36, 73 (see http://www.hp.com/products1/storage/products/disk_arrays/midrange/va7400/infolibrary/product_brief.pdf). I've been told that the VA will format in RAID 1 two 18 GB (unformatted disks) to 16GB for LVM, where as the fc60 (and JBOD, internal disks) go to 17GB. Why is this the case? Or have I been misinformed?...
I've been scouring the web for the armcfg, armdsp, armmgr... commands in the hope they may shed some light on the subject but I can't find any trace of these either!!!
Regards
Tim
Solved! Go to Solution.
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тАО06-19-2002 03:33 AM
тАО06-19-2002 03:33 AM
Re: Why does VA 7xxx use more space when formatting disks
Tim,
Here is a white paper on the math behind the scenes:
http://www.hp.com/products1/storage/products/disk_arrays/infolibrary/mathematics_behind_RAID_5DP.pdf
live free or die
harry
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тАО06-19-2002 03:38 AM
тАО06-19-2002 03:38 AM
Re: Why does VA 7xxx use more space when formatting disks
Tim
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тАО06-19-2002 03:45 AM
тАО06-19-2002 03:45 AM
SolutionFirst, the drive sizes are approximate, and based on the manufacturer's labeling. FOr example, the 73GB drive might actually be 72.5GB. Sometimes they're a little smaller, sometimes a little larger.
Second, the capacity listed is based on a 512-byte block size when formatted. The VA formats them at 520-byte blocks so that it can store additional parity information in every block (it adds an additional CRC to each and every block to ensure data integrity). This also lowers the useable capacity.
The FC60 used different drives, and a different block size, which would account for the slight difference in usable capacity.
To find docs on the arm commands, pull down the .PDF of the Command View SDM users' Guide from www.hp.com - they're in the back.
Good luck!
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тАО06-19-2002 04:05 AM
тАО06-19-2002 04:05 AM
Re: Why does VA 7xxx use more space when formatting disks
Harry & Vincent, as I was re-reading the Maths...RAID5DP paper I ended up going to the white paper on VA one section caught my eye which hints at what Vincent was saying "Data Integrity & High Availablity Fearures".... I quite like the white papers but wish I could use an edit switch to get rid of marketing guff & turn on explain more mode ...
Many thanks 10pts to Harry for the explaiation about block size & extra CRC. quick calculation 16.5 == fc60 assuming 512b is data in 520b block (data+CRC) ... 16.5*512/520 = 16.24, so the maths seems to work out
If any one has any more comments about VA7400 feel free to have your say...
Tim
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тАО06-19-2002 04:17 AM
тАО06-19-2002 04:17 AM
Re: Why does VA 7xxx use more space when formatting disks
You must add (substract) also LVM headers, that are larger as larger are disks.
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тАО06-19-2002 04:41 AM
тАО06-19-2002 04:41 AM
Re: Why does VA 7xxx use more space when formatting disks
Vince, I've looked for the HP Command... & can't find it. It turns out yesterday I was actualy looking at Installation guide for VA7xxx (or words to that effect), it just mentions SDM... If I do a search in HP for "HP Command view SDM Installation and user guide" (as suggested in the Installation guide for VA7xxx....) I gets lots of docs but none are the .pdf I want.
I'll keep digging, unless someone can give me the URL (10 whole points at stake here!!!)
Tim
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тАО06-19-2002 04:49 AM
тАО06-19-2002 04:49 AM
Re: Why does VA 7xxx use more space when formatting disks
You can find manuals under "Support for your product" for all products. (at least most!)
Here's the URL:
http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?contentType=SupportManual&locale=en_US&prodTypeId=12169&prodSeriesId=64112&prodSeriesName=hp+surestore+command+view+sdm&taskName=troubleshoot+a+problem&taskId=8413&prodSeriesId=64112&docIndexName=manuals
There are 2 manuals there. The command 'man' pages start on page 84 of the Installation and User Guide.
Good luck!
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тАО06-19-2002 06:35 AM
тАО06-19-2002 06:35 AM
Re: Why does VA 7xxx use more space when formatting disks
Congratulation one becomming a Wizzard.... I think I just tipped you over the 1,000 pt mark!
Tim
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тАО06-19-2002 07:11 AM
тАО06-19-2002 07:11 AM