Re: [Gluster-devel] GlusterFS performance for random file acess

[Grigory Shamov]

Dear Sam,

Thank you for the quick reply.

Sam Douglas ?????:
> As I understand it, read and write calls in GlusterFS (and FUSE) are
> done with supplied offsets (for example read 8192 bytes at position
> 9024 of the file). This is why seek performance is pretty consistent.
> The rewrite performance with read-ahead and write-behind drops because
> writing to the file changes the modification time and invalidates the
> read-ahead cache. Thus the data that was read was copied needlessly.

So, is there a way to tune it somehow? For now I couldn't think of 
anything except using very small values for the read-ahead cache. With 
page-size of 16K and page-count 1 I get Rewrite of about 7000 K/sec but 
the Sequential Read only about 26000 K/sec which is only a half of the 
best possible value.

--
WBR, Grigory Shamov



>    Sam Douglas
>
> On Dec 19, 2007 10:56 PM, Grigory Shamov <address@hidden> wrote:
> > Dear GlusterFS developers,
> >
> > So I did a Bonnie++ benchmark using one of the servers (Dual Opteron,
> > 4GB RAM, SATA disk, CentOS Linux 5) and a client (old P4 2.4GHz box,
> > 512MB RAM, Gigabit Ethernet, CentOS 4.5). I used 8Gb size for the
> > Bonnie++ tests, and tried either forced flush IO or not (-b option; the
> > data below are for the latter case). Some of the Bonnie++ results are
> > like this:
> >
> > ===============================================
> >   FileSystem:     Sequential Output , K/sec
> >                   Per-char    Block     Rewrite
> > ===============================================
> >   NFS               14442      30419     7710
> >   Lustre            16012      35228     19018
> >   GlusterFS         16582      15833      8358
> >   GlusterFS, wb     17988      43774      8409
> >   GlusterFS, ra     18414      15863      1804
> >   GlusterFS, ra, wb 22403      41821       355
> > ===============================================
> > FileSystem:     Sequential Input, K/sec Random
> >                   Per-char    Block      seeks, #/s
> > ===============================================
> >   NFS               20229      49510      178.8
> >   Lustre            17284      47753       53.0
> >   GlusterFS         16791      16815      161.4
> >   GlusterFS, wb     15304      17438      174.1
> >   GlusterFS, ra     19420      54803      143.3
> >   GlusterFS, ra, wb 19900      54427      144.4
> > ===============================================