Re: RAID6 - whole disk vs partitions

[Steven Haigh <netwiz@crc.id.au>]

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On 20/12/15 07:36, Phil Turmel wrote:
> Hi Steven,
> 
> On 12/19/2015 09:34 AM, Steven Haigh wrote:
> 
>> I've always used the whole disk for the RAID6 - as from what I
>> understand, this gives the best layout for various drives - no matter if
>> they're 512 or 4096 byte sectors.
>>
>> Is this still the case?
> 
> There's no real advantage other than an itty bit of space.  If my case
> was too small to have a separate mirror for my OS, I'd make three
> partitions on everything for boot, LVM root & etc (raid10), and bulk
> storage (raid6).  When I have room for the mirrored OS (boot & LVM), I
> use whole disks for the bulk storage.

Yes, I have two separate disks in RAID1 as the boot / VM guests - the
RAID6 is used for bulk storage. The chassis has a total of 10 hot swap
bays, with 5 used by the RAID6, 2 by the RAID1 and 3 spare. I get resync
speeds of around 170Mb/sec on the RAID1.

>> I've noticed that my resync speeds on this RAID6 hover around 60Mb/sec -
>> which I was expecting to be a bit quicker (although I haven't tested
>> speeds on this array for years).
> 
> Consider using small chunk sizes for parity raid if there's even the
> slightest random access usage.  See the list archives for the past
> couple weeks for a long thread on performance.  There's many
> optimization possibilities.

I have tried to keep up with those couple of threads - but I've found it
hard to follow across the length of time they've been going. A summary
of the findings in those threads with experimentation would be fantastic!

It seems that actual data beyond "increase --setra on /dev/sd[.] and
increase the stripe_cache_size is about all I find via Google - and that
data is years old...

-- 
Steven Haigh

Email: netwiz@crc.id.au
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897


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