Hello there,
I am planning some ext4 filesystems which are currently in (LVM over) a
RAID array having:
stride=1MiB stripe-witdth=4MiB
BUT ... their RAID could be enlarged with more disks in the future
and/or they are likely to be moved around live (leveraging LVM, which I
will align) to other RAIDs which also will have stride=1MiB but unknown,
as of now, stripe-width.
That's on HDDs, with platters.
What do you suggest for stripe-width?
I don't really know how ext4 works, unfortunately. But I think the
answer should be among the following values:
- a) 60MiB: so to be exact multiple of most stripe-widths, in
particular when number of data disks is any of:
1,2,3,4,5,10,12,15,20,30,60 . I expect some longer-than-normal seeks
with HDD heads with 60MiB though.
- b) 7MiB or 11MiB: (prime numbers so *not* likely multiple of most
stripe-widths) so to likely see data eventually spreaded equally on the
various disks (maybe?). That's the opposite reason as (a), so one of
these two must be wrong.
- c) 1MiB so to be exact *divisor* (and not multiple) of all possible
number of disks. This is wrong, isn't it?
- d) use current optimal of 4MiB, then use tune2fs to alter
stripe-width when the underlying stripes are changed. This should be
fine for new writes, but I am not sure what is the impact on reads of
old data.
Thanks for your help
T5
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