[zfs-discuss] Protecting the boot device: Zpool mirror vs hardware RAID

Daniel Davis ddavis at fedora-commons.org
Thu Oct 3 12:28:42 EDT 2013


+1 on MD Raid.  As much as I would like to do a Zpool and have set them
up more than once succesfully, I ran out of time for chasing down
problems during OS updates. And since I am on a EFI/GPT machine, there
are more problems that with a bios boot.  I am using LSI 9207s, EXT4 and
SSDs and MD for boot.  Most reports say the MD Raid is usually (alway
dependent on your specific configuration and use) as fast or faster than
most current hardware solutions, hardware independent and well supported
for troubleshooting.  You don't have to use the boards simple raid
capabilities if you don't want.  The board works great with ZoL purely
as an HBA and can even flashed to IT.  It has very high performance.

With MD Raid you can just use a partition for boot.  You can use the
remainder of the boot disks for other purposes.  While whole disks are
recommended for data zpools, you can still use partitions. You can use
the extra partitions on the boot disks for mirrored zpools, and to
experiment with constructing an rpool, swap et. al.

If you have room in your machine for a couple of inexpensive SSDs
non-hot swap, you can use them for boot and save all or spindle disks
for your "data" zpool.  The LSI board can really make use of the SSDs
speed and you can create log and cache partitions.  The SSDs should be
sufficiently reliable that hot swapping them will likely never happen.

Note, I would still prefer an rpool since I put a lot of configuration
effort into the OS (I am slowly moving to maintaining it with Puppet),
but you likely will need practice and time to get a rpool set up and
keep it working currently on ZoL (no criticism intended - its improving
all the time).

--
Dan Davis



On 10/02/2013 05:18 PM, Bryn Hughes wrote:
> Nothing wrong with using traditional Linux MD RAID for your boot volume. 
>
> You can partition 2 of your drives and just carve off about 512MB for a
> RAID1 MD RAID and use that for /boot, then put everything else in to ZFS.
>
> I personally leave all the OS stuff outside of ZFS.  I definitely want
> my data protected, but I'm not particularly fussed if I have to
> reinstall Linux for some reason.  It's also a lot easier to troubleshoot
> problems or move your data to a different host if you keep the OS and
> your data separate.
>
> Bryn
>
> On 13-10-02 01:48 PM, mickylmartin at gmail.com wrote:
>> I got LSI 9211 because I read ZFS needs more direct access to the
>> disks so an HBA is more suited than a traditional RAID controller,
>> say, Megaraid. 
>> The machines have four hot swap disk slots. But the problem I guess is
>> that the I cannot set up a dual mirror with zpool (RAID 10)  because
>> ZFSOnLinux recommends not to zpool the boot drive. 
>>
>> So the question is, how do I RAID the boot drive and protect that from
>> failures? I guess my only option is to setup a RAID 1 of two drives
>> via the LSI 9211 HBA and boot from that and create a zpool mirror of
>> other two drives. Is that even possible?
>>
>> P.S. Being used to Megraid 9260, I have never really used a real HBA
>> before. Is this HBA 9211 even configurable from BIOS.. not so? Right.
>>
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