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Cashe speed in Raid 1 vs. Raid 10.

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My experience is that Raid 10 is almost dobbel speed as Raid 1. But going from Raid 1 to Raid 10 for the cache drives did not. That is, measuring kvm disk speed. Speed is just slightly better with Raid10. 


Is this as expected?



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What are you comparing? 4 SSDs in btrfs RAID1 vs 4 SSDs in btrfs RAID 10? I wouldn't expect there to be a huge difference because btrfs is intelligent. RAID 10 guarantees that block n is mirrored across two devices and that block n + 1 is mirrored across two different devices. RAID 1 simply guarantees that each block is mirrored across two devices, but when it has four devices to play with it can be quite creative. Though not guaranteed, there's little reason for adjacent blocks not to be written to different devices where possible, so RAID 10-like performance is not unexpected. You can even have configurations that just wouldn't work with conventional RAID, such as a five-device RAID 10, and they don't even all have to be the same capacity!

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54 minutes ago, John_M said:

What are you comparing? 4 SSDs in btrfs RAID1 vs 4 SSDs in btrfs RAID 10? 


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