Re: Re[2]: [zfs-discuss] Re: Recommendation ZFS on StorEdge 3320

[Jonathan Edwards]

On Sep 5, 2006, at 06:45, Robert Milkowski wrote: Hello Wee, Tuesday, September 5, 2006, 10:58:32 AM, you wrote: WYT> On 9/5/06, Torrey McMahon <[EMAIL PROTECTED]> wrote: This is simply not true. ZFS would protect against the same type of errors seen on an individual drive as it would on a pool made of HW raid LUN(s). It might be overkill to layer ZFS on top of a LUN that is already protected in some way by the devices internal RAID code but it does not "make your data susceptible to HW errors caused by the storage subsystem's RAID algorithm, and slow down the I/O". WYT> & Roch's recommendation to leave at least 1 layer of redundancy to ZFS WYT> allows the extension of ZFS's own redundancy features for some truely WYT> remarkable data reliability. WYT> Perhaps, the question should be how one could mix them to get the best WYT> of both worlds instead of going to either extreme. Depends on your data but sometime it could be useful to create HW RAID and then do just striping on ZFS side between at least two LUNs. That way you do not get data protection but fs/pool protection with ditto block. Of course each LUN is HW RAID made of different physical disks. i remember working up a chart on this list about 2 months ago: Here's 10 options I can think of to summarize combinations of zfs with hw redundancy: #   ZFS     ARRAY HW        CAPACITY    COMMENTS --  ---     --------        --------    -------- 1   R0      R1              N/2         hw mirror - no zfs healing (XXX) 2   R0      R5              N-1         hw R5 - no zfs healing (XXX) 3   R1      2 x R0          N/2         flexible, redundant, good perf 4   R1      2 x R5          (N/2)-1     flexible, more redundant, decent perf 5   R1      1 x R5          (N-1)/2     parity and mirror on same drives (XXX) 6   RZ      R0              N-1         standard RAIDZ - no array RAID (XXX) 7   RZ      R1 (tray)       (N/2)-1     RAIDZ+1 8   RZ      R1 (drives)     (N/2)-1     RAID1+Z (highest redundancy) 9   RZ      2 x R5          N-3         triple parity calculations (XXX) 10  RZ      1 x R5          N-2         double parity calculations (XXX) If you've invested in a RAID controller on an array, you might as well take advantage of it, otherwise you could probably get an old D1000 chassis somewhere and just run RAIDZ on JBOD.   If you're more concerned about redundancy than space, with the SUN/STK 3000 series dual controller arrays I would either create at least 2 x RAID5 luns balanced across controllers and zfs mirror, or create at least 4 x RAID1 luns balanced across controllers and use RAIDZ.  RAID0 isn't going to make that much sense since you've got a 128KB txg commit on zfs which isn't going to be enough to do a full stripe in most cases. .je

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