ZFS_DEBUG_MODIFY

All your general support questions for OpenZFS on OS X.

ZFS_DEBUG_MODIFY

Postby Wowfunhappy » Wed Sep 05, 2018 7:06 pm

Hello!

As I imagine is the case for many Mac users, I don't have the ability to use ECC RAM on my machine. To mitigate this somewhat, I'd like to enable the ZFS_DEBUG_MODIFY property, as is recommended by one of ZFS's creators.

Can this be done on macOS? I tried:
Code: Select all
zfs set ZFS_DEBUG_MODIFY=on [dataset]

but that returns
Code: Select all
invalid property 'ZFS_DEBUG_MODIFY'


Maybe I'm just setting this the wrong way? Some Linux-focused tutorials mention editing zfs.conf instead, but I'm not sure what the mac equivalent would be?
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Re: ZFS_DEBUG_MODIFY

Postby lundman » Thu Sep 06, 2018 4:50 pm

Ok So the whole ECC memory thing is totally blown out of proportions. ZFS does not do any worse than any other filesystem without ECC, it just doesn't. But if you are super paranoid about bit corruption, which means ZFS is the only filesystem you can pick (as the other filesystems do no do full checksumming), THEN you should also have ECC. But you don't have to.

Right then, to set "ZFS_DEBUG_MODIFY", it needs to be set in "zfs_flags", which is exported with kstat values, or on osx, sysctl.

"sysctl kstat" to view all kstats, including:

kstat.zfs.darwin.tunable.zfs_flags: 0

Which you can then set with "sysctl kstat.zfs.darwin.tunable.zfs_flags=16" to set ZFS_DEBUG_MODIFY.

However, last time I ran with ZFS_DEBUG_MODIFY, it needed the source to be compiled with DEBUG on, and it did not run well at all (ASSERTS)
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Re: ZFS_DEBUG_MODIFY

Postby Wowfunhappy » Sun Sep 09, 2018 4:32 pm

lundman wrote:Ok So the whole ECC memory thing is totally blown out of proportions. ZFS does not do any worse than any other filesystem without ECC, it just doesn't. But if you are super paranoid about bit corruption, which means ZFS is the only filesystem you can pick (as the other filesystems do no do full checksumming), THEN you should also have ECC. But you don't have to.


Toootally on the same page here, I'll be sleeping perfectly well at night without ECC! It just seemed worth turning this on, at least to do some tests and see what happens.

Anyway, thank you!
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