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StorNext File System Tuning
File Size Mix and Application I/O Characteristics
StorNext File System Tuning Guide 5
example, varying the stripe size and running lmdd with a range of I/O
sizes might be useful to determine an optimal stripe size multiple to
configure the SNFS
StripeBreadth.
Some storage vendors now provide RAID6 capability for improved
reliability over RAID5. This may be particularly valuable for SATA disks
where bit error rates can lead to disk problems. However, RAID6
typically incurs a performance penalty compared to RAID5, particularly
for writes. Check with your storage vendor for RAID5 versus RAID6
recommendations.
File Size Mix and Application I/O Characteristics
It is always valuable to understand the file size mix of the target dataset
as well as the application I/O characteristics. This includes the number of
concurrent streams, proportion of read versus write streams, I/O size,
sequential versus random, Network File System (NFS) or Common
Internet File System (CIFS) access, and so on.
For example, if the dataset is dominated by small or large files, various
settings can be optimized for the target size range.
Similarly, it might be beneficial to optimize for particular application I/O
characteristics. For example, to optimize for sequential 1MB I/O size it
would be beneficial to configure a stripe group with four 4+1 RAID5
LUNs with 256K stripe size.
However, optimizing for random I/O performance can incur a
performance trade-off with sequential I/O.
Furthermore, NFS and CIFS access have special requirements to consider
as described in the Direct Memory Access (DMA) I/O Transfer
section.
Direct Memory Access
(DMA) I/O Transfer 0
To achieve the highest possible large sequential I/O transfer throughput,
SNFS provides DMA-based I/O. To utilize DMA I/O, the application
must issue its reads and writes of sufficient size and alignment. This is
called well-formed I/O. See the
mount command settings
auto_dma_read_length and auto_dma_write_length, described in the
Mount Command Options
on page 19.