Wilkinson, Alex wrote:
0n Thu, Apr 30, 2009 at 11:11:55AM -0500, Bob Friesenhahn wrote:
>On Thu, 30 Apr 2009, Wilkinson, Alex wrote:
>>
>> I currently have a single 17TB MetaLUN that i am about to present to an
>> OpenSolaris initiator and it will obviously be ZFS. However, I am
constantly
>> reading that presenting a JBOD and using ZFS to manage the RAID is best
>> practice ? Im not really sure why ? And isn't that a waste of a high
performing
>> RAID array (EMC) ?
>
>The JBOD "advantage" is that then ZFS can schedule I/O for the disks
>and there is less chance of an unrecoverable pool since ZFS is assured
>to lay out redundant data on redundant hardware and ZFS uses more
>robust error detection than the firmware on any array. When using
>mirrors there is considerable advantage since writes and reads can be
>concurrent.
>
>That said, your EMC hardware likely offers much nicer interfaces for
>indicating and replacing bad disk drives. With the ZFS JBOD approach
>you have to back-track from what ZFS tells you (a Solaris device ID)
>and figure out which physical drive is not behaving correctly. EMC
>tech support may not be very helpful if ZFS says there is something
>wrong but the raid array says there is not. Sometimes there is value
>with taking advantage of what you paid for.
So, shall I forget ZFS and use UFS ?
Can you share more of your system configuration / intended use?
UFS has a limitation of 16TB max for a single filesystem and this
filesystem is limited to ~1 million inodes per TB roughly. So you
if want to store a lot of small files you may find you have a problem. I
have certainly run into this limitation on numerous occasions.
(Smaller than ~1TB has a very high limit for inodes and generally isn't
an issue)
Beyond what I mentioned in my other post it is hard to recommend
anything else. ZFS does tend to have higher hardware
requirements than UFS and doesn't perform particularly well with low
amounts of RAM. But without more workload
information it is pretty hard to advise the best path that you should take.
-aW
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