Question re ZFS with mixed drive speeds & types

Jacques Foucry jacques+freebsd at
Wed Aug 5 18:26:53 UTC 2020

Le mercredi 05 août 2020 à 01:32:02 (-0700), David Christensen à écrit:
> On 2020-08-04 23:55, Greg Marsh wrote:
> > Hello everyone. I hope you are well.
> > 
> > I’m budgeting to upgrading my home file server. Sort of for more data capacity, but mostly for more physical space, flexibility and to try some things storage wise. It’s currently got a 6x2tb SATA raidz of WD reds w/ssd for l2arc & logging.
> > 1st goal - mirror that ssd.
> > 
> > Now, I’ve got a big box of still working Seagate Cheetah 15k scsi drives & several controllers, both raid and not. The drives are only 146gb, but 15k. However, I’m wondering if I were to make a VDEV pool of like 7 of them, add that to my volume and what, if any positive benefit it might to my ZFS storage?
> > 
> > I ask because about 10 years ago, I was involved in a project that had a HUGE storage component. Many of the vendors we brought in to pitch, including Sun, were promoting tiered storage. Sun in particular were quite proud of this tech. Their system ran ZFS and had a hybrid of ssd, sas & SATA, with the system dynamically moving data around the different speed/capacity drives, based on their activity, all transparent to the application or user. Most often used data coming from the ssd & sas drives, with less active files kept on the SATA drives.

I remember the same thing when Sun demostrate us ZFS (I was a Sunkskill at
this time). But I never tried.

> > 
> > I’m wondering if this capability made it into the open source version of ZFS. Because that would be fantastic.
> > 
> > Thank you all for any insight or advice.
> > 
> > Cheers,
> > Greg
> Everything I have read recommends using the same size and speed devices 
> in a given pool.
> To upgrade a pool, one technique is to replace one device at a time with 
> a "better" device, wait for the new device to resilver, and repeat until 
> all devices have been upgraded.  Beware that if you have raidz1, you 
> would be at risk of losing everything if a drive failed while upgrading 
> another.

If you want I wrote a small tuto about that and change my Free∇AS disks.

> Using the SSD for cache and using two or more SCSI drives in a mirror 
> for log makes sense if you want to minimize hardware cost.
> David
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Jacques Foucry

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