Yes, I think it would be a great topic for the summit. --John
On Jan 14, 2013, at 7:54 AM, Tong Li <[email protected]> wrote: > John and swifters, > I see this problem as a big problem and I think that the scenario described > by Alejandro is a very common scenario. I am thinking if it is possible to > have like two rings (one with the newer extended power, one with the existing > ring power), when significant changes made to the hardware, partition, a new > ring get started with a command, and new data into Swift will use the new > ring, and existing data on the existing ring still available and slowly (not > impact the normal use) but automatically moves to the new ring, once the > existing ring shrinks to the size zero, then that ring can be removed. The > idea is to sort of having two virtual Swift systems working side by side, the > migration from existing ring to new ring being done without interrupting the > service. Can we put this topic/feature as one to be discussed during the next > summit and to be considered as a high priority feature to work on for coming > releases? > > Thanks. > > Tong Li > Emerging Technologies & Standards > Building 501/B205 > [email protected] > > <graycol.gif>John Dickinson ---01/11/2013 04:28:47 PM---If effect, this would > be a complete replacement of your rings, and that is essentially a whole new c > > From: John Dickinson <[email protected]> > To: Alejandro Comisario <[email protected]>, > Cc: "[email protected]" > <[email protected]>, openstack > <[email protected]> > Date: 01/11/2013 04:28 PM > Subject: Re: [Openstack] [SWIFT] Change the partition power to recreate > the RING > Sent by: [email protected] > > > > If effect, this would be a complete replacement of your rings, and that is > essentially a whole new cluster. All of the existing data would need to be > rehashed into the new ring before it is available. > > There is no process that rehashes the data to ensure that it is still in the > correct partition. Replication only ensures that the partitions are on the > right drives. > > To change the number of partitions, you will need to GET all of the data from > the old ring and PUT it to the new ring. A more complicated, but perhaps more > efficient) solution may include something like walking each drive and > rehashing+moving the data to the right partition and then letting replication > settle it down. > > Either way, 100% of your existing data will need to at least be rehashed (and > probably moved). Your CPU (hashing), disks (read+write), RAM (directory > walking), and network (replication) may all be limiting factors in how long > it will take to do this. Your per-disk free space may also determine what > method you choose. > > I would not expect any data loss while doing this, but you will probably have > availability issues, depending on the data access patterns. > > I'd like to eventually see something in swift that allows for changing the > partition power in existing rings, but that will be hard/tricky/non-trivial. > > Good luck. > > --John > > > On Jan 11, 2013, at 1:17 PM, Alejandro Comisario > <[email protected]> wrote: > > > Hi guys. > > We've created a swift cluster several months ago, the things is that righ > > now we cant add hardware and we configured lots of partitions thinking > > about the final picture of the cluster. > > > > Today each datanodes is having 2500+ partitions per device, and even tuning > > the background processes ( replicator, auditor & updater ) we really want > > to try to lower the partition power. > > > > Since its not possible to do that without recreating the ring, we can have > > the luxury of recreate it with a very lower partition power, and rebalance > > / deploy the new ring. > > > > The question is, having a working cluster with *existing data* is it > > possible to do this and wait for the data to move around *without data > > loss* ??? > > If so, it might be true to wait for an improvement in the overall cluster > > performance ? > > > > We have no problem to have a non working cluster (while moving the data) > > even for an entire weekend. > > > > Cheers. > > > > > > [attachment "smime.p7s" deleted by Tong Li/Raleigh/IBM] > _______________________________________________ > Mailing list: https://launchpad.net/~openstack > Post to : [email protected] > Unsubscribe : https://launchpad.net/~openstack > More help : https://help.launchpad.net/ListHelp >
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