[zfs-discuss] raidz1 or raidz2

Steve Costaras stevecs at chaven.com
Sat Nov 3 23:19:28 EDT 2012



Correct, unlike traditional raid, ZFS keeps a used block map so it only needs to sync/create hashes for blocks that are actually used.  

 
>-----Original Message-----
>From: Marcus Sorensen [mailto:shadowsor at gmail.com]
>Sent: Saturday, November 3, 2012 08:57 PM
>To: zfs-discuss at zfsonlinux.org
>Subject: Re: [zfs-discuss] raidz1 or raidz2
>
>So for example, if I have 100G data on a 3 disk raidz, the resilver should
>be the same whether they are 3t drives or 1t drives ( ignoring the slight
>differences in platter density affecting speed)
>On Nov 3, 2012 7:54 PM, "Marcus Sorensen" <shadowsor at gmail.com> wrote:
>
>> Doesn't resilver depend on data size rather than disk size? When I pull a
>> disk from my three way mirror and replace it, it takes all of five minutes
>> to resilver a 320GB drive and zfs status reports that it resolve red the
>> data size.
>> On Nov 2, 2012 11:09 AM, "Christ Schlacta" <aarcane at aarcane.org> wrote:
>>
>>> Gordan, I was under the impression that resilver time scaled with disk
>>> size, and not count. The 4 day period should be the same on any raid zn
>>> configuration he chooses
>>> On Nov 2, 2012 10:01 AM, "Gordan Bobic" <gordan.bobic at gmail.com> wrote:
>>>
>>>> On 11/02/2012 04:34 PM, Brian Menges wrote:
>>>>
>>>>> Recalling an older post:
>>>>> http://mail.opensolaris.org/**pipermail/zfs-discuss/2010-**
>>>>> September/044701.html<http://mail.opensolaris.org/pipermail/zfs-discuss/2010-September/044701.html>
>>>>>
>>>>> SNIP ---
>>>>> RAIDZ2 vdevs should have 4, 6, or 10 devices in each vdev
>>>>> RAIDZ3 vdevs should have 5, 7, or 11 devices in each vdev
>>>>> SNIP ---
>>>>>
>>>>> My recommendation would be to use RaidZ2 with 10 devices per vdev; this
>>>>> fits nicely with 60 disks assuming that they're all for the pool. Given
>>>>> they're 3tb disks, I'd strongly suggest RaidZ2 over RaidZ1 for previously
>>>>> noted reasons - reslivering will murder this array. RaidZ3 is appealing,
>>>>> but you're going to have to declare some spares at that point (and by
>>>>> declaring spares, I mean leave them alone - blank non-allocated devs since
>>>>> spares are still broken in rc11 to my knowledge). In a RaidZ3 I'd suggest 7
>>>>> devices per vdev, times 8 means you'd use 56 drives, you'll have 4 spares
>>>>> available.
>>>>>
>>>>> Recap
>>>>>
>>>>> Raidz2 - 10 devices per vdev, 6 vdevs
>>>>> Raidz3 - 7 devices per vdev, 8 vdevs, 4 remaining devices as "spares"
>>>>>
>>>>
>>>> (8+2)x3TB is pushing your luck, IMO. You are looking at resilvering time
>>>> of about 4-5 days. I wouldn't use more than 4+2 with disks that are so
>>>> large.
>>>>
>>>> Gordan
>>>>
>>>
>




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