[@test]# time cat 50b.img > /dev/null real 0m0.004s user 0m0.000s sys 0m0.002s [@test]# time cat 50b.img > /dev/null real 0m0.002s user 0m0.000s sys 0m0.002s [@test]# time cat 50b.img > /dev/null real 0m0.002s user 0m0.000s sys 0m0.001s [@test]# time cat 50b.img > /dev/null real 0m0.002s user 0m0.001s sys 0m0.001s [@test]# Luminous, centos7.6 kernel cephfs mount, 10Gbit, ssd meta, hdd data, mds 2,2Ghz -----Original Message----- From: Alexandre DERUMIER [mailto:aderumier@xxxxxxxxx] Sent: 18 January 2019 15:37 To: Burkhard Linke Cc: ceph-users Subject: Re: CephFS - Small file - single thread - read performance. Hi, I don't have so big latencies: # time cat 50bytesfile > /dev/null real 0m0,002s user 0m0,001s sys 0m0,000s (It's on an ceph ssd cluster (mimic), kernel cephfs client (4.18), 10GB network with small latency too, client/server have 3ghz cpus) ----- Mail original ----- De: "Burkhard Linke" <Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> À: "ceph-users" <ceph-users@xxxxxxxxxxxxxx> Envoyé: Vendredi 18 Janvier 2019 15:29:45 Objet: Re: CephFS - Small file - single thread - read performance. Hi, On 1/18/19 3:11 PM, jesper@xxxxxxxx wrote: > Hi. > > We have the intention of using CephFS for some of our shares, which > we'd like to spool to tape as a part normal backup schedule. CephFS > works nice for large files but for "small" .. < 0.1MB .. there seem to > be a "overhead" on 20-40ms per file. I tested like this: > > root@abe:/nfs/home/jk# time cat /ceph/cluster/rsyncbackups/13kbfile > > /dev/null > > real 0m0.034s > user 0m0.001s > sys 0m0.000s > > And from local page-cache right after. > root@abe:/nfs/home/jk# time cat /ceph/cluster/rsyncbackups/13kbfile > > /dev/null > > real 0m0.002s > user 0m0.002s > sys 0m0.000s > > Giving a ~20ms overhead in a single file. > > This is about x3 higher than on our local filesystems (xfs) based on > same spindles. > > CephFS metadata is on SSD - everything else on big-slow HDD's (in both > cases). > > Is this what everyone else see? Each file access on client side requires the acquisition of a corresponding locking entity ('file capability') from the MDS. This adds an extra network round trip to the MDS. In the worst case the MDS needs to request a capability release from another client which still holds the cap (e.g. file is still in page cache), adding another extra network round trip. CephFS is not NFS, and has a strong consistency model. This comes at a price. Regards, Burkhard _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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