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From: Michael Laajanen on 26 Mar 2010 09:55 Hi, A ZFS vdev should be up to 9 disk I have read, what is the disadvantage with having 16 disk in one vdev, compared to two vdevs with 8 disk each all set to raidz2? I would save 2 disk by having only one vdev. /michael
From: Ian Collins on 26 Mar 2010 17:33 On 03/27/10 02:55 AM, Michael Laajanen wrote: > Hi, > > A ZFS vdev should be up to 9 disk I have read, what is the disadvantage > with having 16 disk in one vdev, compared to two vdevs with 8 disk each > all set to raidz2? Two important things will suffer: Performance: will suck compared to a stripe of smaller vdevs. Reliability: you expose your self to a much greater risk or multiple drive failures. Resilver times will also be slower, compounding the risk. -- Ian Collins
From: Michael Laajanen on 27 Mar 2010 14:55 Hi, Ian Collins wrote: > On 03/27/10 02:55 AM, Michael Laajanen wrote: >> Hi, >> >> A ZFS vdev should be up to 9 disk I have read, what is the disadvantage >> with having 16 disk in one vdev, compared to two vdevs with 8 disk each >> all set to raidz2? > > Two important things will suffer: > > Performance: will suck compared to a stripe of smaller vdevs. What is the optimal number of disks in a vdev? > > Reliability: you expose your self to a much greater risk or multiple > drive failures. Resilver times will also be slower, compounding the risk. > Then the HBAs must also be concidered I guess. /michael
From: Ian Collins on 27 Mar 2010 15:17 On 03/28/10 07:55 AM, Michael Laajanen wrote: > Hi, > > Ian Collins wrote: >> On 03/27/10 02:55 AM, Michael Laajanen wrote: >>> Hi, >>> >>> A ZFS vdev should be up to 9 disk I have read, what is the disadvantage >>> with having 16 disk in one vdev, compared to two vdevs with 8 disk each >>> all set to raidz2? >> >> Two important things will suffer: >> >> Performance: will suck compared to a stripe of smaller vdevs. > What is the optimal number of disks in a vdev? It depends what you want to do with the pool. I never go beyond 8 in a raidz2 configuration. >> Reliability: you expose your self to a much greater risk or multiple >> drive failures. Resilver times will also be slower, compounding the risk. >> > Then the HBAs must also be concidered I guess. Not really, they fail way less often than drives. -- Ian Collins
From: Michael Laajanen on 28 Mar 2010 09:25
Hi, Ian Collins wrote: > On 03/28/10 07:55 AM, Michael Laajanen wrote: >> Hi, >> >> Ian Collins wrote: >>> On 03/27/10 02:55 AM, Michael Laajanen wrote: >>>> Hi, >>>> >>>> A ZFS vdev should be up to 9 disk I have read, what is the disadvantage >>>> with having 16 disk in one vdev, compared to two vdevs with 8 disk each >>>> all set to raidz2? >>> >>> Two important things will suffer: >>> >>> Performance: will suck compared to a stripe of smaller vdevs. > >> What is the optimal number of disks in a vdev? > > It depends what you want to do with the pool. I never go beyond 8 in a > raidz2 configuration. > So I have a E450 with 16 300G drives so having two vdevs of 8 drives each then for me if I would do the same setup. I was thinking of raidz2 with all the 16 in one vdev saving 600GB. >>> Reliability: you expose your self to a much greater risk or multiple >>> drive failures. Resilver times will also be slower, compounding the >>> risk. >>> >> Then the HBAs must also be concidered I guess. > > Not really, they fail way less often than drives. > /michael |