Hi Guys, I have a "portable pool" i.e. one that I carry around in an enclosure. However, any SSD I add for L2ARC, will not be carried around... meaning the cache drive will become unavailable from time to time. My question is.... Will random removal of the cache drive put the pool into a "degraded" state or affect the integrity of the pool at all? Additionally, how adversely will this effect "warm up"... Or will moving the enclosure between machines with and without cache, just automatically work, and offer benefits when cache is available, and less benefits when it isn''t? I hope this question isn''t too much of a rambling :) thanks.
On 10/14/12 10:02, Michael Armstrong wrote:> Hi Guys, > > I have a "portable pool" i.e. one that I carry around in an enclosure. However, any SSD I add for L2ARC, will not be carried around... meaning the cache drive will become unavailable from time to time. > > My question is.... Will random removal of the cache drive put the pool into a "degraded" state or affect the integrity of the pool at all? Additionally, how adversely will this effect "warm up"... > Or will moving the enclosure between machines with and without cache, just automatically work, and offer benefits when cache is available, and less benefits when it isn''t?Why bother with cache devices at all if you are moving the pool around? As you hinted above, the cache can take a while to warm up and become useful. You should zpool remove the cache device before exporting the pool. -- Ian.
Ok, so it is possible to remove. Good to know, thanks . I move the pool maybe once a month for a few days, on an otherwise daily used fixed location. So thought the warm up allowance may be worth it. I guess I just wanted to know if adding a cache device was a one way operation or not and whether or not it risked integrity. Sent from my iPhone On 13 Oct 2012, at 23:02, Ian Collins <ian at ianshome.com> wrote:> On 10/14/12 10:02, Michael Armstrong wrote: >> Hi Guys, >> >> I have a "portable pool" i.e. one that I carry around in an enclosure. However, any SSD I add for L2ARC, will not be carried around... meaning the cache drive will become unavailable from time to time. >> >> My question is.... Will random removal of the cache drive put the pool into a "degraded" state or affect the integrity of the pool at all? Additionally, how adversely will this effect "warm up"... >> Or will moving the enclosure between machines with and without cache, just automatically work, and offer benefits when cache is available, and less benefits when it isn''t? > > Why bother with cache devices at all if you are moving the pool around? As you hinted above, the cache can take a while to warm up and become useful. > > You should zpool remove the cache device before exporting the pool. > > -- > Ian. >
2012-10-14 2:41, Michael Armstrong wrote:> Ok, so it is possible to remove. Good to know, thanks . I move the pool maybe once a month for a few days, on an otherwise daily used fixed location. So thought the warm up allowance may be worth it. I guess I just wanted to know if adding a cache device was a one way operation or not and whether or not it risked integrity.I haven''t *tried* your scenario, but I *believe* that: 1) Loss of L2ARC should not be fatal to a pool - reads should just fall back to main pool, so even an occasional export without removal should work; 2) Removal and addition of L2ARC on the fly does work - tested that ;) 3) As of now, upon pool import (and/or L2ARC attachment) the cache device is considered empty. So any such porting of the disk, as well as reboots of the computer, will cause new cache warm-up (and some SSD wear). 4) If your portable disk is USB and practically limited by the bus and protocol, you may have benefits from caching of its hot data in RAM and SSD (ARC and L2ARC) - if the data from this pool is used heavily enough. //Jim