Re: striping of a 4 drive raid10

[Neil Brown <neilb@suse.de>]

On Sunday January 27, keld@dkuug.dk wrote:
> Hi
> 
> I have tried to make a striping raid out of my new 4 x 1 TB
> SATA-2 disks. I tried raid10,f2 in several ways:
> 
> 1: md0 = raid10,f2 of sda1+sdb1, md1= raid10,f2 of sdc1+sdd1, md2 = raid0
> of md0+md1
> 
> 2: md0 = raid0 of sda1+sdb1, md1= raid0 of sdc1+sdd1, md2 = raid01,f2
> of md0+md1
> 
> 3: md0 = raid10,f2 of sda1+sdb1, md1= raid10,f2 of sdc1+sdd1, chunksize of 
> md0 =md1 =128 KB,  md2 = raid0 of md0+md1 chunksize = 256 KB
> 
> 4: md0 = raid0 of sda1+sdb1, md1= raid0 of sdc1+sdd1, chunksize
> of md0 = md1 = 128 KB, md2 = raid01,f2 of md0+md1 chunksize = 256 KB
> 
> 5: md0= raid10,f4 of sda1+sdb1+sdc1+sdd1

Try
  6: md0 = raid10,f2 of sda1+sdb1+sdc1+sdd1

Also try raid10,o2 with a largeish chunksize (256KB is probably big
enough).

NeilBrown


> 
> My new disks give a transfer rate of about 80 MB/s, so I expected
> to have something like 320 MB/s for the whole raid, but I did not get
> more than about 180 MB/s.
> 
> I think it may be something with the layout, that in effect 
> the drives should be something like:
> 
>           sda1             sdb1    sdc1      sdd1
>            0                1       2         3
>            4                5       6         7
> 
> And this was not really doable for the combination of raids,
> because thet combinations give different block layouts.
> 
> How can it be done? Do we need a new raid type?
> 
> Best regards
> keld
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