In my deployment I part the disk for wal and db seperately as I can assign the size manually. For example, I assign every two partitions of nvme with 30G and 2G, for each osd's wal and db. Tony Liu <tonyliu0592@xxxxxxxxxxx> 于2020年8月28日周五 上午1:53写道： > How's WAL utilize disk when it shares the same device with DB? > Say device size 50G, 100G, 200G, they are no difference to DB > because DB will take 30G anyways. Does it make any difference > to WAL? > > Thanks! > Tony > > -----Original Message----- > > From: Zhenshi Zhou <deaderzzs@xxxxxxxxx> > > Sent: Wednesday, August 26, 2020 11:16 PM > > To: Tony Liu <tonyliu0592@xxxxxxxxxxx> > > Cc: Anthony D'Atri <anthony.datri@xxxxxxxxx>; ceph-users@xxxxxxx > > Subject: Re: Re: Add OSD with primary on HDD, WAL and DB on > > SSD > > > > Official document says that you should allocate 4% of the slow device > > space for block.db. > > > > But the main problem is that Bluestore uses RocksDB and RocksDB puts a > > file on the fast device only if it thinks that the whole layer will fit > > there. > > > > As for RocksDB, L1 is about 300M, L2 is about 3G, L3 is near 30G, and L4 > > is about 300G. > > For instance, RocksDB puts L2 files to block.db only if it’s at least 3G > > there. > > As a result, 30G is a acceptable value. > > > > Tony Liu <tonyliu0592@xxxxxxxxxxx <mailto:tonyliu0592@xxxxxxxxxxx> > > > 于2020年8月25日周二 上午10:49写道： > > > > > > > -----Original Message----- > > > From: Anthony D'Atri <anthony.datri@xxxxxxxxx > > <mailto:anthony.datri@xxxxxxxxx> > > > > Sent: Monday, August 24, 2020 7:30 PM > > > To: Tony Liu <tonyliu0592@xxxxxxxxxxx > > <mailto:tonyliu0592@xxxxxxxxxxx> > > > > Subject: Re: Re: Add OSD with primary on HDD, WAL > > and DB on > > > SSD > > > > > > Why such small HDDs? Kinda not worth the drive bays and power, > > instead > > > of the complexity of putting WAL+DB on a shared SSD, might you > > have been > > > able to just buy SSDs and not split? ymmv. > > > > 2TB is for testing, it will bump up to 10TB for production. > > > > > The limit is a function of the way the DB levels work, it’s not > > > intentional. > > > > > > WAL by default takes a fixed size, like 512 MB or something. > > > > > > 64 GB is a reasonable size, it accomodates the WAL and allows > > space for > > > DB compaction without overflowing. > > > > For each 10TB HDD, what's the recommended DB device size for both > > DB and WAL? The doc recommends 1% - 4%, meaning 100GB - 400GB for > > each 10TB HDD. But given the WAL data size and DB data size, I am > > not sure if that 100GB - 400GB will be used efficiently. > > > > > With this commit the situation should be improved, though you > > don’t > > > mention what release you’re running > > > > > > https://github.com/ceph/ceph/pull/29687 > > > > I am using ceph version 15.2.4 octopus (stable). > > > > Thanks! > > Tony > > > > > >>> I don't need to create > > > >>> WAL device, just primary on HDD and DB on SSD, and WAL will > > be using > > > >>> DB device cause it's faster. Is that correct? > > > >> > > > >> Yes. > > > >> > > > >> > > > >> But be aware that the DB sizes are limited to 3GB, 30GB and > > 300GB. > > > >> Anything less than those sizes will have a lot of untilised > > space, > > > >> e.g a 20GB device will only utilise 3GB. > > > > > > > > I have 1 480GB SSD and 7 2TB HDDs. 7 LVs are created on SSD, > > each is > > > > about 64GB, for 7 OSDs. > > > > > > > > Since it's shared by DB and WAL, DB will take 30GB and WAL will > > take > > > > the rest 34GB. Is that correct? > > > > > > > > Is that size of DB and WAL good for 2TB HDD (block store and > > object > > > > store cases)? > > > > > > > > Could you share a bit more about the intention of such limit? > > > > > > > > > > > > Thanks! > > > > Tony > > > > _______________________________________________ > > > > ceph-users mailing list -- ceph-users@xxxxxxx <mailto:ceph- > > users@xxxxxxx> To unsubscribe send an > > > > email to ceph-users-leave@xxxxxxx <mailto:ceph-users- > > leave@xxxxxxx> > > > > _______________________________________________ > > ceph-users mailing list -- ceph-users@xxxxxxx <mailto:ceph- > > users@xxxxxxx> > > To unsubscribe send an email to ceph-users-leave@xxxxxxx > > <mailto:ceph-users-leave@xxxxxxx> > > > > _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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