ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks

[Damien Fleuriot]

Well actually...

raidz2:
- 7x 1.5 tb = 10.5tb
- 2 parity drives

raidz1:
- 3x 1.5 tb = 4.5 tb
- 4x 1.5 tb = 6 tb , total 10.5tb
- 2 parity drives in split thus different raidz1 arrays

So really, in both cases 2 different parity drives and same storage...

---
Fleuriot Damien

On 5 Jan 2011, at 16:55, Chris Forgeron <cforgeron at acsi.ca> wrote:

> First off, raidz2 and raidz1 with copies=2 are not the same thing. 
> 
> raidz2 will give you two copies of parity instead of just one. It also guarantees that this parity is on different drives. You can sustain 2 drive failures without data loss. 
> 
> raidz1 with copies=2 will give you two copies of all your files, but there is no guarantee that they are on different drives, and you can still only sustain 1 drive failure.
> 
> You'll have better space efficiency with raidz2 if you're using 9 drives. 
> 
> If I were you, I'd use your 9 disks as one big raidz, or better yet, get 10 disks, and make a stripe of 2 5 disk raidz's for the best performance. 
> 
> Save your SSD drive for the L2ARC (cache) or ZIL, you'll get better speed that way instead of throwing it away on a boot drive. 
> 
> --
> 
> 
> -----Original Message-----
> From: owner-freebsd-stable at freebsd.org [mailto:owner-freebsd-stable at freebsd.org] On Behalf Of Damien Fleuriot
> Sent: January-05-11 5:01 AM
> To: Damien Fleuriot
> Cc: freebsd-stable at freebsd.org
> Subject: Re: ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks
> 
> Hi again List,
> 
> I'm not so sure about using raidz2 anymore, I'm concerned for the performance.
> 
> Basically I have 9x 1.5T sata drives.
> 
> raidz2 and 2x raidz1 will provide the same capacity.
> 
> Are there any cons against using 2x raidz1 instead of 1x raidz2 ?
> 
> I plan on using a SSD drive for the OS, 40-64gb, with 15 for the system itself and some spare.
> 
> Is it worth using the free space for cache ? ZIL ? both ?
> 
> @jean-yves : didn't you experience problems recently when using both ?
> 
> ---
> Fleuriot Damien
> 
> On 3 Jan 2011, at 16:08, Damien Fleuriot <ml at my.gd> wrote:
> 
>> 
>> 
>> On 1/3/11 2:17 PM, Ivan Voras wrote:
>>> On 12/30/10 12:40, Damien Fleuriot wrote:
>>> 
>>>> I am concerned that in the event a drive fails, I won't be able to 
>>>> repair the disks in time before another actually fails.
>>> 
>>> An old trick to avoid that is to buy drives from different series or 
>>> manufacturers (the theory is that identical drives tend to fail at 
>>> the same time), but this may not be applicable if you have 5 drives 
>>> in a volume :) Still, you can try playing with RAIDZ levels and probabilities.
>>> 
>> 
>> That's sound advice, although one also hears that they should get 
>> devices from the same vendor for maximum compatibility -.-
>> 
>> 
>> Ah well, next time ;)
>> 
>> 
>> A piece of advice I shall heed though is using 1% less capacity than 
>> what the disks really provide, in case one day I have to swap a drive 
>> and its replacement is a few kbytes smaller (thus preventing a rebuild).
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