> On Jun 17, 2015, at 3:48 AM, InterNetX - Juergen Gotteswinter > <[email protected]> wrote: > > With with default Settings you will end up in Caching everything twice > with ZFS inside the Guest.
This statement is true for every file system, except maybe HSFS or FAT16. In and of itself, this is not enough of a reason to use or not use any particular file system. > > Either use some regular, legacy FS or change primary/secondarycache to > Metadata only Again, these are not likely to be important. The reason is that to the underlying ZFS, the data cached in the KVM client is only seen once. This means it gets in the MRU side of the ARC and is thus more likely to be evicted first. Inside the KVM client, if running ZFS then the hot data will be cached in the MFU side of the ARC. In other words, the concept of double-caching is not a binary choice and for a busy server with memory pressure, you can expect that most data won't be double-cached. -- richard > > Am 17.06.2015 um 12:20 schrieb David Finster: >> Hi Perttu >> >> We don’t run any Linux inside KVMs, but we do run a fair amount of >> Windows. In general, your right in that running ZFS inside a KVM isn’t >> going to get you any benefit and would probably be detrimental. It is >> worth noting that all writes from inside a KVM are considered >> synchronous anyway as far as the ‘zones’ pool is concerned. Any writes >> that your guest does will be immediately committed to some disk (hence >> the importance of an SLOG). >> >> ZFS snapshots are consistent when created, but I guess there is the >> potential for some application inside the VM to have writes outstanding >> when a snapshot is taken (through queued IO?). If that were the case, >> then you would need some mechanism of notifying the application that >> it’s about to be snapped to be completely safe. >> >> That being said, anything that uses a proper transaction log should be >> fine. I’ve done snapshots of SQL and Exchange servers and >> migrations/test emergency restores have been fine. Doing a snapshot of a >> live VM and then bringing it up on another host is similar to it >> experiencing a power failure, which is what the transaction logs are >> designed to handle. >> >> As Ian mentioned, you might also be better off giving LX zones a go - >> they are much friendlier to the host and no additional file systems are >> involved. >> >> - Dave >> >>> On 17 Jun 2015, at 8:00 PM, Perttu <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Hello SmartOS community, long time follower, first time poster here. >>> >>> What do you guys think are best practices regarding file systems in >>> KVM Linux guests? >>> >>> Is it advisable to use ZFS inside guests? Wouldn’t it use double the >>> memory for the same data? >>> >>> Or would using something like XFS or ext4 be better and perhaps tuning >>> them to be more synchronous if crash resiliency is wanted? >>> >>> My main concern is data integrity if I snapshot and send the guest >>> regularly to another host for disaster recovery. Performance is also >>> important but I do have a slog device (S3700). >>> >>> Cheers, >>> Perttu >>> *smartos-discuss* | Archives >>> <https://www.listbox.com/member/archive/184463/=now> >>> <https://www.listbox.com/member/archive/rss/184463/25738179-216c4b5f> >>> | Modify <https://www.listbox.com/member/?&;> Your Subscription >>> [Powered by Listbox] <http://www.listbox.com/> >>> >> >> *smartos-discuss* | Archives >> <https://www.listbox.com/member/archive/184463/=now> >> <https://www.listbox.com/member/archive/rss/184463/26910370-9cc4a721> | >> Modify >> <https://www.listbox.com/member/?&;> >> Your Subscription [Powered by Listbox] <http://www.listbox.com> >> > > > ------------------------------------------- > smartos-discuss > Archives: https://www.listbox.com/member/archive/184463/=now > RSS Feed: https://www.listbox.com/member/archive/rss/184463/21953302-fd56db47 > Modify Your Subscription: https://www.listbox.com/member/?&; > Powered by Listbox: http://www.listbox.com ------------------------------------------- smartos-discuss Archives: https://www.listbox.com/member/archive/184463/=now RSS Feed: https://www.listbox.com/member/archive/rss/184463/25769125-55cfbc00 Modify Your Subscription: https://www.listbox.com/member/?member_id=25769125&id_secret=25769125-7688e9fb Powered by Listbox: http://www.listbox.com
