Bharathram Sivasubramanian
2015-Apr-11 01:56 UTC
[Gluster-users] Question on file reads from a distributed replicated volume
Thanks, Krutika! So, if I understand you correctly...if both Brick 1 and Brick 2 have a good copy of the file, then we can't tell for sure if the file will be read only from Brick 1 all the time and not Brick 2? in other words, for read#1, the file could be read from brick 2 and for another read which could happen a few minutes later, the file could be read from brick 1? ________________________________ From: Krutika Dhananjay <kdhananj at redhat.com> Sent: Friday, April 10, 2015 9:30 PM To: Bharathram Sivasubramanian Cc: Gluster-users at gluster.org Subject: Re: [Gluster-users] Question on file reads from a distributed replicated volume ________________________________ From: "Bharathram Sivasubramanian" <Bharathram.Sivasubramanian at vantrix.com> To: Gluster-users at gluster.org Sent: Saturday, April 11, 2015 3:03:48 AM Subject: [Gluster-users] Question on file reads from a distributed replicated volume Let us assume that we have a distributed replicated gluster volume with 4 bricks. Brick 1 is replicating its data with Brick 2 and Brick 3 is replicating its data with Brick 4. Suppose a file called aa.txt is present and replicated on Bricks 1 & 2. A gluster client would like to read this file. Which brick will the file come from? In other words: - Will the file always be fetched from brick 1? - Will the file always be fetched from brick 2? - Will the file be fetched from brick 1 or 2 depending on the attempt? i.e. is there some load balancing where sometimes the file comes from brick 1 and at other times the file will come from brick 2? A given file will consistently be "read" from one of the N (in this case 2) replicas, as long as it holds a good copy of the file (that which does not need heal), even with client restart. We call it the "read child" of the file. Load balancing within a volume is done across different files wherein different files would have different but constant read children. -Krutika _______________________________________________ Gluster-users mailing list Gluster-users at gluster.org http://www.gluster.org/mailman/listinfo/gluster-users -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.gluster.org/pipermail/gluster-users/attachments/20150411/cbaad616/attachment.html>
Krutika Dhananjay
2015-Apr-11 02:07 UTC
[Gluster-users] Question on file reads from a distributed replicated volume
----- Original Message -----> From: "Bharathram Sivasubramanian" <Bharathram.Sivasubramanian at vantrix.com> > To: "Krutika Dhananjay" <kdhananj at redhat.com> > Cc: Gluster-users at gluster.org > Sent: Saturday, April 11, 2015 7:26:27 AM > Subject: Re: [Gluster-users] Question on file reads from a distributed > replicated volume> Thanks, Krutika!> So, if I understand you correctly...if both Brick 1 and Brick 2 have a good > copy of the file, then we can't tell for sure if the file will be read only > from Brick 1 all the time and not Brick 2? in other words, for read#1, the > file could be read from brick 2 and for another read which could happen a > few minutes later, the file could be read from brick 1?Nope. For a given file, read requests will always be served from the same brick. This means that in your example, both read #1 and read #2 will served from the same brick, which is the read child of the file. In 3.6.0 and above, the read child of a file is computed by applying a hash function on its GFID, which means it is always guaranteed to give the same value (because the gfid of a file will remain the same throughout its lifetime, needless to say). -Krutika> From: Krutika Dhananjay <kdhananj at redhat.com> > Sent: Friday, April 10, 2015 9:30 PM > To: Bharathram Sivasubramanian > Cc: Gluster-users at gluster.org > Subject: Re: [Gluster-users] Question on file reads from a distributed > replicated volume> ----- Original Message -----> > From: "Bharathram Sivasubramanian" <Bharathram.Sivasubramanian at vantrix.com> > > > To: Gluster-users at gluster.org > > > Sent: Saturday, April 11, 2015 3:03:48 AM > > > Subject: [Gluster-users] Question on file reads from a distributed > > replicated > > volume >> > Let us assume that we have a distributed replicated gluster volume with 4 > > bricks. Brick 1 is replicating its data with Brick 2 and Brick 3 is > > replicating its data with Brick 4. Suppose a file called aa.txt is present > > and replicated on Bricks 1 & 2. A gluster client would like to read this > > file. Which brick will the file come from? In other words: >> > - Will the file always be fetched from brick 1? >> > - Will the file always be fetched from brick 2? >> > - Will the file be fetched from brick 1 or 2 depending on the attempt? i.e. > > is there some load balancing where sometimes the file comes from brick 1 > > and > > at other times the file will come from brick 2? >> A given file will consistently be "read" from one of the N (in this case 2) > replicas, as long as it holds a good copy of the file (that which does not > need heal), even with client restart. We call it the "read child" of the > file. Load balancing within a volume is done across different files wherein > different files would have different but constant read children.> -Krutika> > _______________________________________________ > > > Gluster-users mailing list > > > Gluster-users at gluster.org > > > http://www.gluster.org/mailman/listinfo/gluster-users >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.gluster.org/pipermail/gluster-users/attachments/20150410/666600a6/attachment.html>
Joe Julian
2015-Apr-11 02:18 UTC
[Gluster-users] Question on file reads from a distributed replicated volume
Do, "gluster volume set help". There is a pretty good explanation of the read subvolume preferences and options. On April 10, 2015 6:56:27 PM PDT, Bharathram Sivasubramanian <Bharathram.Sivasubramanian at vantrix.com> wrote:>Thanks, Krutika! > > >So, if I understand you correctly...if both Brick 1 and Brick 2 have a >good copy of the file, then we can't tell for sure if the file will be >read only from Brick 1 all the time and not Brick 2? in other words, >for read#1, the file could be read from brick 2 and for another read >which could happen a few minutes later, the file could be read from >brick 1? > >________________________________ >From: Krutika Dhananjay <kdhananj at redhat.com> >Sent: Friday, April 10, 2015 9:30 PM >To: Bharathram Sivasubramanian >Cc: Gluster-users at gluster.org >Subject: Re: [Gluster-users] Question on file reads from a distributed >replicated volume > > > >________________________________ >From: "Bharathram Sivasubramanian" ><Bharathram.Sivasubramanian at vantrix.com> >To: Gluster-users at gluster.org >Sent: Saturday, April 11, 2015 3:03:48 AM >Subject: [Gluster-users] Question on file reads from a distributed > replicated volume > >Let us assume that we have a distributed replicated gluster volume with >4 bricks. Brick 1 is replicating its data with Brick 2 and Brick 3 is >replicating its data with Brick 4. Suppose a file called aa.txt is >present and replicated on Bricks 1 & 2. A gluster client would like to >read this file. Which brick will the file come from? In other words: > >- Will the file always be fetched from brick 1? > >- Will the file always be fetched from brick 2? > >- Will the file be fetched from brick 1 or 2 depending on the >attempt? i.e. is there some load balancing where sometimes the file >comes from brick 1 and at other times the file will come from brick 2? > >A given file will consistently be "read" from one of the N (in this >case 2) replicas, as long as it holds a good copy of the file (that >which does not need heal), even with client restart. We call it the >"read child" of the file. Load balancing within a volume is done across >different files wherein different files would have different but >constant read children. > >-Krutika >_______________________________________________ >Gluster-users mailing list >Gluster-users at gluster.org >http://www.gluster.org/mailman/listinfo/gluster-users > > > >------------------------------------------------------------------------ > >_______________________________________________ >Gluster-users mailing list >Gluster-users at gluster.org >http://www.gluster.org/mailman/listinfo/gluster-users-- Sent from my Android device with K-9 Mail. Please excuse my brevity. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.gluster.org/pipermail/gluster-users/attachments/20150410/299fc77b/attachment.html>