Re: GlusterFS performance for random file acess

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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 <gas@xxxxxx> 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
===============================================





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