FreeBSD ZFS file server with SSD HDD

[Frank Leonhardt (m)]

On 13 October 2017 14:43:16 BST, Kate Dawson <k4t at 3msg.es> wrote:
>On Fri, Oct 13, 2017 at 01:04:50PM +0100, Frank Leonhardt (m) wrote:
>> 
>> 
>> This all matters A LOT if you're using ZFS to back a virtual HD for a
>VM. Things lke vSphere  make every NFS write synchronous. Given the
>guest OS is probably using a file format that makes this pointless adds
>insult to injury. ZFS writing every block to a CoW file will fragment
>it all to hell and back.
>> 
>> So, throwing hardware at it isn't going to solve the underlying
>problem. You need to sort out the sync writes. If your file store is on
>a UPS, ignore them (I comment out the code). And store your virtual HD
>on UFS if possible. 
>
>Thanks,
>
>sync is disabled on the dataset, I think it's all async.  The VM's all
>have journalled files systems, and the the system is UPS backed.
>
>NFS is mounted async - I think that is the default for Debian Linux
>
>My understanding is that ZFS will always be consistent, however in the
>case of catastrophic shutdown some data may not be written to disk, and
>we will just have to take our chances.
>
>A key reason for ZFS being chosen was snapshots.  Otherwise I think
>GNU/Linux would have been chosen over FreeBSD and ZFS
>
>Thanks for the detailed info on ZIL/SLOG
>
>
>Regards, 
>
>Kate Dawson
>> -- 
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>
>-- 
>"The introduction of a coordinate system to geometry is an act of
>violence"

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