On 01/12/09 20:45, Simon wrote:> Hi Experts,
>
> IHAC who using Solaris 10 + ZFS,two questions they''re concerned:
>
> - ZIL(zfs intent log) is enabled by default for ZFS,there are varied
> storage purchased by customer(such as EMC CX/DMX series,HDS AMS/USP
> series and etc),customer wonder whether there is any impact to these
> storages if enable ZIL,if have,what is the negative factors?
As far as I know there hasn''t been any performance reports comparing
various devices specifically for ZFS or the ZIL. Richard Elling may know?
>
> - Under what circumstances,should I disable zil ?
- It''s not recommended to ever disable it! It was originally added as a
switch to allow the new ZIL to be disabled if it proved unstable. It should
have been removed shortly afterwards. If the system loses power or crashes
then some recent synchronous changes that were claimed to be safely on disk
might not be. If you know this then I suppose you could take advantage of the
speed and redo the recent changes. For instance, it has been suggested that
Solaris
binaries be built with the ZIL disabled. If the system crashes then the build
would be started again from scratch. Panics are sufficiently rare and the build
time can be cut significantly (eg 30%). However, these are somewhat
contrived circumstances and I wouldn''t recommend ever configuring a
customers
system with the ZIL disabled.
A safer option is to turn off disk write cache flushing (set
zfs:zfs_nocacheflush=1).
This should only be done if it''s known *all* zpool devices are
non-volatile.
This has almost the same performance effect as disabling the ZIL, as
it''s
the actual writing of the bits to the rotating rust that takes most of the time.
This also helps speed up other writes - ie committing transaction groups.
>
> - If the device used by zpool is come from above listed external storage
> (EMC or HDS),what size is suggested for storage LUN ?
> As current rules,customer uses 100G for EMC CX,and 55G/110G for EMC DMX,
> and 52G for HDS USP V,100G for HDS AMS as LUN size,the filesystem over
> LUNs is UFS.
Sorry - I don''t know.
>
> Any reply are much appreciated,thanks in advance.
>
> Best Rgds,
> Simon
>
>
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