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List:       zfs-discuss
Subject:    Re: [zfs-discuss] Thin device support in ZFS?
From:       David Magda <dmagda () ee ! ryerson ! ca>
Date:       2009-12-31 21:53:39
Message-ID: 98ABEEA8-E0E0-4E10-BE11-0E75755D61BD () ee ! ryerson ! ca
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On Dec 31, 2009, at 13:44, Joerg Schilling wrote:

> ZFS is COW, but does the SSD know which block is "in use" and which  
> is not?
>
> If the SSD did know whether a block is in use, it could erase unused  
> blocks
> in advance. But what is an "unused block" on a filesystem that  
> supports
> snapshots?

Personally, I think that at some point in the future there will need  
to be a command telling SSDs that the file system will take care of  
handling blocks, as new FS designs will be COW. ZFS is the first  
"mainstream" one to do it, but Btrfs is there as well, and it looks  
like Apple will be making its own FS.

Just as the first 4096-byte block disks are silently emulating 4096 - 
to-512 blocks, SSDs are currently re-mapping LBAs behind the scenes.  
Perhaps in the future there will be a setting to say "no really, I'm  
talking about the /actual/ LBA 123456".

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