Hello All,
We're doing a fresh Lustre 1.8.4 install using Sun StorageTek 2540
arrays for our OST targets. We've configured these as RAID6 with no
spares which means we have the equivalent of 10 data disks and 2 parity
disks in play on each OST.
We configured the "Segment Size" on these arrays at 512 KB. I believe
this is equivalent to the "chunk size" in the Lustre operations manual
(section 10.1.1). Based on the formulae in the manual: in order to have
my stripe width fall below 1MB; I need to reconfigure my "Segment Size"
like this:
Segment Size <= 1024KB/(12-2) = 102.4 KB
so 16KB, 32KB or 64KB are optimal values
Does this seem right?
Do I really need to do this (reinitialize the arrays/volumes) to get my
Segment Size below 1MB? What impact will/won't this have on performance?
When I format the OST filesystem; I need to provide options for both
stripe and stride. The manual indicates that the units for these values
are 4096-byte (4KB) blocks. Given that, I should use something like:
-E stride= (one of)
16KB/4KB = 4
32KB/4KB = 8
64KB/4KB = 16
stripe= (one of)
16KB*10/4KB = 40
32KB*10/4KB = 80
64KB*10/4KB = 160
so for example I would issue the following:
mkfs.lustre --mountfsoptions="stripe=160" --mkfsoptions="-E stride=16 -m
1" ...
Is it better for to opt for the higher values or lower values here?
Also, does anyone have recommendations for "aligning" the filesystem so
that the fs blocks align with the RAID chunks? We've done things like
this for SSD drives. We'd normally give Lustre the entire RAID device
(without partitions) so this hasn't been an issue in the past. For this
installation though; we're creating multiple volumes (for size/space
reasons) so partitioning is a necessary evil now.
Thanks for any feedback!
-Ed Walter
Carnegie Mellon University
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