[OpenIndiana-discuss] What happens when a ZIL drive dies?

[Bob Friesenhahn]

On Thu, 7 Jun 2012, Matt Clark wrote:

> That's true, but if you look at slides 24 & 25 of 
> http://www.ddrdrive.com/zil_accelerator.pdf you'll see seek 
> distributions for a SLOG device with the ZILs for five filesystems - 
> although each ZIL is broadly append only (slides 21 and 22), there 
> is still a lot of seeking going on.  Of course if you only had one 
> active FS on a pool, the activity would be almost pure append, so 
> sequential write performance would be the most important factor.

Agreed.  I posted my response out of fear that someone might construe 
your statement as meaning that the ZIL is also used to satisfy reads.

Bob

>
> On 7 Jun 2012, at 00:10, Bob Friesenhahn wrote:
>
>> On Wed, 6 Jun 2012, Matt Clark wrote:
>>
>>> Yes, it's interesting to consider the possible real world performance.  ZIL writes, even by DDRDrive's stats, are very closely clustered around the tail of the ZIL, with most seeks being to near locations - it's certainly not going to seek more than 8 gig away. So probably just leaving it at one big partition would be fine too.
>>
>> The ZIL is not used for anything but to replay pending synchronous writes if the system unexpectedly reboots.  It is not used as a source of data while the system is running.  It is normally a write-only device.
>>
>
>
>
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-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/