The saga continues

[Warren Block]

On Wed, 7 Oct 2015, William A. Mahaffey III wrote:

> On 10/07/15 19:32, Warren Block wrote:
>> On Wed, 7 Oct 2015, William A. Mahaffey III wrote:
>> 
>>>> Please read the warning at the top of that page.  The Handbook shows the 
>>>> right way of using gmirror(8).  My page on it mirrors GPT partitions, 
>>>> which is likely to be a problem if one of the drives ever fails.  If you 
>>>> absolutely have to use gmirror(8) with GPT, use only one partition per 
>>>> drive.
>>>> 
>>> 
>>> 
>>> Can I partition the drives using '-s MBR', then mirror some of the 
>>> partitions & create '-s BSD' slices inside of those mirrors ?
>> 
>> Ow, my brain.  Why are you simultaneously creating safe data storage along 
>> with ultra-unsafe data storage?  What is the end goal?
>> 
>> Multiple mirrors between drive partitions is potentially dangerous. 
>> Consider that drives often die only a few days or hours apart.  Now think 
>> of a two-drive system with multiple mirrored partitions.  One drive has 
>> died.  Put in a new drive, create the multiple partitions on it, and add 
>> them to the mirrors.  All of them start replicating at the same time, 
>> putting a big load on the original still-working drive.  The drive that is 
>> the same age as the drive that failed...
>
> Creating the safe storage for the system so I could (hopefully) get it 
> rebooted & reconstructed if 1 of the 2 HDD's croaks. If your scenario happens 
> (both HDD's croak almost together, or the 2nd one croaks under the load of 
> replicating), I'm fried anyway. That also argues against any mirroring at 
> all, same thing happens if I mirror both drives as per the handbook.

The difference is that multiple mirrored partitions that are replicating 
at the same time put both drives under lots of head contention.  It will 
also make it take much, much longer.

>>> Specifically, I would partition each drive into 4 primary partitions, 
>>> /boot, swap, 1 partition to be mirrored & then sliced up as per the 
>>> handbook, & 1 partition to be striped & then sliced up ? I would probably 
>>> mirror /boot as well, if feasible. It seems this might comport w/ all of 
>>> the restrictions & possible meta-data conflicts, but I am definitely out 
>>> of my area, hence the questions. TIA & have a good one.
>> 
>> /boot is a directory in /, the boot partition is just a place to store 
>> bootcode.  They are separate things.
>
> Agreed, bad nomenclature on my part .... it would be boot-partition, swap, 
> mirrored-partition & striped partition.
>
>> 
>> What is the function of the RAID0 here?  Can it be replaced with tmpfs or 
>> maybe an SSD?
>
>
> To maximize available space for storing movies, etc. I would be slicing it 
> into 2 slices, for /usr/local & /home. All stuff here would be backed up 
> elsewhere on the LAN and/or recreatable. I just want the largest possible 
> pool of GiB's available.

ZFS with a RAIDZ1 is a reasonable compromise.  Three drives instead of 
two, the space of two drives, any one drive can fail but the array still 
works.