[Lustre-discuss] clarification on mkfs.lustre options
Sebastian Gutierrez
gutseb at cs.stanford.edu
Thu Jul 29 23:42:37 PDT 2010
Hello
This will probably be a pretty basic question however I wanted to verify that I was understanding the documentation correctly.
The enclosure I am using supports 15 disks. We have initially ordered 6 disks + hostpare. I think my recommendation is going to be a 6 disk raid 6. Which will give us a 4 data disk raid set plus 2 parity disks. Later we will have the option to create another 6 disk raid6 or expand the current raid set to a 10 disk raid 6 then move the journal to a 4 disk raid 1/0 and have 1 disk hot spare.
The current Raid 6 will have a 128k chunksize (lustre terminology)
this gives us:
<stripe_width> = <chunksize> * (<disks> - <parity_disks>) <=1MB
512K <= 128k*4
<chunksize> <= 1024kB/4; either 256k, 128k, 64k
256k = < = 1024k/4k
<chunk_blocks> = <chunksize(decided above)> / 4k
32 = 256/4
128k = 512k / 4k
<stripe_width_blocks> = <stripe_width> / 4k
Therefore
My mkfs options should be
--mkfsoptions="-E stripe=128 -E stride=32" /dev/sdb
upgrade options:
The filesystem chunk_block options would still be valid since the chunk_blocks would stay the same.
purchase 6 more disks
This will allow for a new raid 6 that is aligned the same way with 3 hotspares.
or (I need clarification if this understanding is correct)
purchase 10 more disks
Expand the current raid 6 to a larger 10 disk/raid 6 with a 4 disk raid 1/0 for a external journal plus a hot spare.
Is my understanding of the documentation accurate?
Do both of these options seem like potential upgrade options?
Cheers,
Sebastian
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