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Old 10-17-2009, 04:03 PM   #1
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ISCSI target image sizing

Hello all

I wasn't sure where to post this question because it does overlap a few areas.

Could somebody please tell me how to use dd to create an image file for an iscsi target considering the follwoing info :

Following an ubuntu tutorial here: (great how to by the way --so easy and fast)

I got this
mkdir /storage
dd if=/dev/zero of=/storage/lun1.img bs=1024k count=20000

I understand that the block size is 1024k and the count is 20000 records (right or wrong ?)

But what's confusing to me is what is the best block size (bs) and number of records (count) for a specific image size.

Is it a fairly good idea to maintain a 1024k block size ?

Could someone shed some light (explain) on the block sizes and performance of each considering a file of say 30GB 50GB 100GB 200GB 300GB 400GB and 500GB or even 1TB.

Would it be a good idea to create several smaller files and declare them as LUN's on the iscsi target or rather have one large file?

The reason I am asking all of this is becuase my plan is to have have the ubuntu box run iscsitarget with a 1TB hard drive containing the .img file(s) created using dd.
I will then mirror the 1TB drive using a software mirror.
The 1TB hard drives are SATA.

Would really love some feedback or help from others using ISCSITARGET or openiscsi target
Old 10-19-2009, 02:05 AM   #2
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If you're using image files the block size while running 'dd' isn't relevant, 'dd' isn't creating a file system just a file. The block size of the underlying file system could be important but that's already in place so it's a bit late to change it.

I haven't tested but it may also impact performance by having the extra layer of abstraction when using image files rather than presenting a raw partition/volume,

HTH... cheers



count, dd, image, img, iscsi

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