Michelle Sullivan
http://www.mhix.org/
Sent from my iPad
> On 03 May 2019, at 22:51, Kevin P. Neal <k...@neutralgood.org> wrote:
> 
> On Fri, May 03, 2019 at 08:25:08PM +1000, Michelle Sullivan wrote:
>>> On 03 May 2019, at 20:09, Borja Marcos via freebsd-stable 
>>> <freebsd-stable@freebsd.org> wrote:
>>> 
>>> 
>>> 
>>>> On 3 May 2019, at 11:55, Pete French <petefre...@ingresso.co.uk> wrote:
>>>> 
>>>> 
>>>> 
>>>>> On 03/05/2019 08:09, Borja Marcos via freebsd-stable wrote:
>>>>> 
>>>>> The right way to use disks is to give ZFS access to the plain CAM 
>>>>> devices, not thorugh some so-called JBOD on a RAID
>>>>> controller which, at least for a long time, has been a *logical* “RAID0” 
>>>>> volume on a single disk. That additional layer can
>>>>> completely break the semantics of transaction writes and cache flushes.
>>>>> With some older cards it can be tricky to achieve, from patching source 
>>>>> drivers to enabling a sysctl tunable or even
>>>>> flashing the card to turn it into a plain HBA with no RAID features (or 
>>>>> minimal ones).
>>>> 
>>>> Oddly enough I got bitten by something like this yesteray. I have a 
>>>> machine containing an HP P400 RAID controller, which is nice enough, but I 
>>>> run ZFS so I have made the drives all into RAID-0 as being as close as I 
>>>> can get to accessing the raw SAS drives.
>> 
>> I got bitten by that on this hardware originally...  switching to raid-0 and 
>> separate drives then switching to write-through (not write back and 
>> definitely not write back with bad bbu) seemed to solve it.
> 
> I have an old Dell R610 with a PERC 6/i and Megaraid SAS driver Ver 4.23.
> When I use mfiutil to set caching to write through it still goes through
> the cache. Which means that if a drive fails and the machine reboots the
> firmware stops the boot because it has data in the cache that it wants
> to store on the failed drive. So a normal failure of a drive in a three
> way ZFS mirror that shouldn't cause a loss of service actually does.
> 


I don’t think it will do that in write through.. it will everytime in write 
back.

> Thumbs down to RAID cards.
> -- 
> Kevin P. Neal                                http://www.pobox.com/~kpn/
> 
> "Good grief, I've just noticed I've typed in a rant. Sorry chaps!"
>                            Keir Finlow Bates, circa 1998
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