Hi Dominic, I should have mentioned that I've set noatime already. I have not found any obvious other mount options that would contribute to 'write on read' behaviour.. Thx Samy > On 29 Jan 2020, at 15:43, DHilsbos@xxxxxxxxxxxxxx wrote: > > Sammy; > > I had a thought; since you say the FS has high read activity, but you're seeing large write I/O... is it possible that this is related to atime (Linux last access time)? If I remember my Linux FS basics, atime is stored in the file entry for the file in the directory, and I believe directory information is stored in the metadata pool (dentries?). > > As a test; you might try mounting the CephFS with the noatime flag. Then see if the write I/O is reduced. > > I honestly don't know if CephFS supports atime, but I would expect it would. > > Thank you, > > Dominic L. Hilsbos, MBA > Director - Information Technology > Perform Air International Inc. > DHilsbos@xxxxxxxxxxxxxx > www.PerformAir.com > > > > -----Original Message----- > From: Samy Ascha [mailto:samy@xxxxxx] > Sent: Wednesday, January 29, 2020 2:25 AM > To: ceph-users@xxxxxxx > Subject: Write i/o in CephFS metadata pool > > Hi! > > I've been running CephFS for a while now and ever since setting it up, I've seen unexpectedly large write i/o on the CephFS metadata pool. > > The filesystem is otherwise stable and I'm seeing no usage issues. > > I'm in a read-intensive environment, from the clients' perspective and throughput for the metadata pool is consistently larger than that of the data pool. > > For example: > > # ceph osd pool stats > pool cephfs_data id 1 > client io 7.6 MiB/s rd, 19 KiB/s wr, 404 op/s rd, 1 op/s wr > > pool cephfs_metadata id 2 > client io 338 KiB/s rd, 43 MiB/s wr, 84 op/s rd, 26 op/s wr > > I realise, of course, that this is a momentary display of statistics, but I see this unbalanced r/w activity consistently when monitoring it live. > > I would like some insight into what may be causing this large imbalance in r/w, especially since I'm in a read-intensive (web hosting) environment. > > Some of it may be expected in when considering details of my environment and CephFS implementation specifics, so please ask away if more details are needed. > > With my experience using NFS, I would start by looking at client io stats, like `nfsstat` and tuning e.g. mount options, but I haven't been able to find such statistics for CephFS clients. > > Is there anything of the sort for CephFS? Are similar stats obtainable in some other way? > > This might be a somewhat broad question and shallow description, so yeah, let me know if there's anything you would like more details on. > > Thanks a lot, > Samy > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to 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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