On Thu, 10 May 2007, mike wrote:
> The host for this is up in the air. I'd hope I could use a Shuttle XPC.
>
> It's an 8 drive USB enclosure. The total bandwidth to all 8 drives
> would be 480Mbps, which is fine for me. I was hoping to do a RAID-Z or
> RAID-Z2. I would have it export the drives as JBOD.
>
> http://fwdepot.com/thestore/product_info.php/products_id/1623
My personal opinion is that USB is not robust enough under (Open)Solaris
to provide the reliability that someone considering ZFS is looking for.
I base this on experience with two 7 port powered USB hubs, each with 4 *
2Gb Kingston flash drives, connected via 2 ports to a Solaris (update 3)
desktop box which runs ZFS on two internal 500Gb drives. I see about 24
to 28Mb/Sec (bytes) maximum of bandwidth over each USB bus. One time,
after disconnecting one hub (to show someone the hub with 4*USB drives) it
hung the OS and reset the box. A subsequent import of the ZFS volume that
was disconnected, failed. (Yes it was exported, but failed to import).
So my take on USB is ... it's not sufficiently robust - and a USB related
failure is likely to cause loss of the entire ZFS dataset; i.e., its
likely to trash more that one drive in a raidz config.
I'd be interested in hearing other opinions on USB connected drives
under (Open)Solaris ....
> If I get my math right and understand ZFS... If I have 8x750 gig disks
> using RAID-Z I will have 7x750 space available. This will provide
> standard RAID-5 style redundancy. (6x750 for RAID-Z2)
Correct.
> My confusion is that I see a lot of people suggesting cutting it up
> for mirrored RAID-Z setups. The main reason for this is performance
> right? I am fine with standard USB 2.0 performance and RAID-5 (or 6)
Usually, because you want to take advantage of the operational
characteristics of different storage topologies to meet different end
uses. For example, on one server here, with 10 SATA disk drives, they are
configured as:
- a 5-way raidz
- a 3-way zfs mirror
- a 2-way zfs mirror
The 5-way raidz is ideal when you want to re-assemble a DVD image after
downloading 5 *.zip components - and other operations requiring large
file, mainly sequencial access type, work patterns. The 3-way mirror is
ideal for software development activity and where data reliability is of
paramount importance. The 2-way mirror is a good general purpose
all-arounder.
But there is "overlap", in terms of usability/applicability, between all
these configurations. But ZFS allows you to easily setup different
configs and evaluate their operational characteristics based on *your*
usage scenario. That is one of the beautiful characteristics of the well
engineered and highly user friendly ZFS human interface.
> functionality but with the added capability of data integrity
> checking/self-healing/etc/etc. I don't need to build some crazy array.
> Just something for SOHO use, sharing files over samba to a couple
> Windows machines + a media player.
Suggestion - try two 4-way raidz pools.
> Side note: Is this right? "ditto" blocks are extra parity blocks
> stored on the same disk (won't prevent total disk failures, but could
> provide data recovery if enough parity is available)
Yes. See Richard Ellings' excellent blog titled "ZFS, copies, and data
protection", where one picture is truely worth 1,000 words.
Regards,
Al Hopper Logical Approach Inc, Plano, TX. [EMAIL PROTECTED]
Voice: 972.379.2133 Fax: 972.379.2134 Timezone: US CDT
OpenSolaris Governing Board (OGB) Member - Apr 2005 to Mar 2007
http://www.opensolaris.org/os/community/ogb/ogb_2005-2007/
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