Database Reference
In-Depth Information
Serial Performance as a Function of Blocksize
300
250
200
XFS
GPFS
150
100
50
0
Block Size
(a)
Effect of Block Alignment on GPFS Performance (each blocksize)
200
180
160
140
120
100
80
60
40
20
0
maxbw
minbw
aligned bw
128
256
512
1024
2048
4096
8192
16384
32768
Block Size (bytes)
(b)
Figure 1.4
This figure (a) compares a cluster file system (GPFS) to the local
file system performance (XFS) for varying transaction sizes for contiguous,
append-only streaming writes. Figure (b) shows that the performance of disk
devices, even for relatively large transaction sizes, is substantially impacted
by the alignment of the data transfers relative to the native block boundaries
of the disk device.
large-scale systems, which will be described in much more detail in Chapter 2
of this topic. Figure 1.4(a) compares a cluster file system (GPFS) to the local
file system performance (XFS) for varying transaction sizes for contiguous,
append-only streaming writes using POSIX I/O. Given the huge performance
disparity between best and worst performance shown on this plot, even a sin-
gle small transaction interspersed with large transactions can substantially
lower the average delivered performance. Small I/O transactions, even for lin-
ear operations, can be extremely costly because the entire disk-block must be
transferred even when a small subset of the data is updated.
