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I felt a bit stupid; I re-read the important parts several times but failed to visualize what that looks like on the disks, and how blocks are reconstructed on

I felt a bit stupid; I re-read the important parts several times but failed to visualize what that looks like on the disks, and how blocks are reconstructed on disk failure. A little googling lead me to a paper by Intel[0] which has a simple visualization of how this works on page 11, in case I'm not the only one. [0] https://docplayer.net/117362530-Draid-declustered-raid-for-zfs-installation-and-configuration-guide-high-performance-data-division.html https://docplayer.net/117362530-Draid-declustered-raid-for-z...

aaronax 6y ago
Yeah that is a good link; I especially liked the text on page 7. I believe Windows Storage Spaces has long used a similar technique[0] too, though it has been a few years since I was looking into it. I wonder if ZFS DRAID will eventually allow full utilization of disks of mixed sizes too, that was always a very attractive feature of Storage Spaces to me. [0] https://techcommunity.microsoft.com/t5/storage-at-microsoft/deep-dive-the-storage-pool-in-storage-spaces-direct/ba-p/425959 https://techcommunity.microsoft.com/t5/storage-at-microsoft/...
robert_foss 6y ago
Ah, so a distributed redundancy drive instead of a dedicated one as with normal raid.
knorker 6y ago
Oh? When I first saw that illustration it hugely frustrated me about how poor that illustration is. The numbers are not explained, nor are the rows, or columns. And the numbers repeat. I saw the diagrams first outside of that pdf, though. Still, the way it goes "4, 8, 2, 16, 1, and so on..." is a boatload of "wat?".
- abrookewood 6y ago
  I think this quote makes it clearer: "unlike the raidz1 configuration shown above, in the dRAID1 configuration the neighbor drives of the failed drive 0 (i.e. drives in a same data+parity group) are not fixed". So the RAIDZ is set up with fixed groups of drives, but the dRAID is not, even though the parity ratio is the same.
  - knorker 6y ago
    Yeah, I get it. But the illustrations I found terrible. Those images did not speak a 1000 words. In fact they are just confusing. Your comment explains it better than the illustration.

aaronax 6y ago

Yeah that is a good link; I especially liked the text on page 7. I believe Windows Storage Spaces has long used a similar technique[0] too, though it has been a few years since I was looking into it. I wonder if ZFS DRAID will eventually allow full utilization of disks of mixed sizes too, that was always a very attractive feature of Storage Spaces to me. [0] https://techcommunity.microsoft.com/t5/storage-at-microsoft/deep-dive-the-storage-pool-in-storage-spaces-direct/ba-p/425959 https://techcommunity.microsoft.com/t5/storage-at-microsoft/...

robert_foss 6y ago

Ah, so a distributed redundancy drive instead of a dedicated one as with normal raid.

knorker 6y ago

Oh? When I first saw that illustration it hugely frustrated me about how poor that illustration is. The numbers are not explained, nor are the rows, or columns. And the numbers repeat. I saw the diagrams first outside of that pdf, though. Still, the way it goes "4, 8, 2, 16, 1, and so on..." is a boatload of "wat?".

abrookewood 6y ago
I think this quote makes it clearer: "unlike the raidz1 configuration shown above, in the dRAID1 configuration the neighbor drives of the failed drive 0 (i.e. drives in a same data+parity group) are not fixed". So the RAIDZ is set up with fixed groups of drives, but the dRAID is not, even though the parity ratio is the same.
- knorker 6y ago
  Yeah, I get it. But the illustrations I found terrible. Those images did not speak a 1000 words. In fact they are just confusing. Your comment explains it better than the illustration.