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On 9 Feb 2010, at 15:27, J. Roeleveld wrote: |
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> On Tuesday 09 February 2010 16:11:14 Stroller wrote: |
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>> On 9 Feb 2010, at 13:57, J. Roeleveld wrote: |
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>>> ... |
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>>> With Raid (NOT striping) you can remove one disk, leaving the Raid- |
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>>> array in a |
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>>> reduced state. Then repartition the disk you removed, repartition |
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>>> and then re- |
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>>> add the disk to the array. |
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>> |
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>> Exactly. Except the partitions extend, in the same positions, across |
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>> all the disks. |
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>> |
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>> You cannot remove one disk from the array and repartition it, because |
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>> the partition is across the array, not the disk. The single disk, |
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>> removed from a RAID 5 (specified by Paul Hartman) array does not |
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>> contain any partitions, just one stripe of them. |
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>> |
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>> I apologise if I'm misunderstanding something here, or if your RAID |
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>> works differently to mine. |
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> |
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> Stroller, it is my understanding that you use hardware raid adapters? |
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Yes. |
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> If that is the case, then the mentioned method won't work for you ... |
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> |
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> I believe Paul Hartman is, like me, using Linux Sofware raid (mdadm |
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> +kernel |
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> drivers). |
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> |
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> In that case, you can do either of the following: |
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> Put the whole disk into the RAID, eg: |
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> mdadm --create --level=5 --devices=6 /dev/sd[abcdef] |
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> Or, you create 1 or more partitions on the disk and use these, eg: |
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> mdadm --create --level=5 --devices=6 /dev/sd[abcdef]1 |
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Thank you for identifying the source of this misunderstanding. |
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> and if your raid-adapters already align everything properly, then |
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> you shouldn't notice any problems with these drives. |
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> It would, however, be interesting to know how hardware raid adapters |
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> handle these 4KB sector-sizes. |
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I think my adaptor at least, being older, may very well be prone to |
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this problem. I discussed this in my post of 8 February 2010 19:57:46 |
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GMT - certainly I have a RAID array aligned beginning at sector 63, |
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and it is at least a little slow. I will test just as soon as I can |
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afford 3 x 1TB drives. |
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I think the RAID adaptor would have to be quite "clever" to avoid this |
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problem. It may be a feature added in newer controllers, but that |
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would be a special attempt to compensate. I think in the general case |
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the RAID controller should just consolidate 3 x physical block devices |
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(or more) into 1 x virtual block device, and should not do anything |
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more complicated that this. I am sure that a misalignment will |
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propagate downwards through the levels of obscusification. |
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IMO this is a fdisk "bug". A feature should be added so that it tries |
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to align optimally in most circumstances. RAID controllers should not |
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be trying to do anything clever to accommodate potential misalignment |
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unless it is really cheap to do so. |
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Stroller. |
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