> On Mar 23, 2016, at 7:49 AM, Richard Jahnel <rjah...@ellipseinc.com> wrote: > > It should be noted that using a 512e disk as a 512n disk subjects you to a > significant risk of silent corruption in the event of power loss. Because > 512e disks does a read>modify>write operation to modify 512byte chunk of a 4k > sector, zfs won't know about the other 7 corrupted 512e sectors in the event > of a power loss during a write operation. So when discards the incomplete txg > on reboot, it won't do anything about the other 7 512e sectors it doesn't > know were affected.
Disagree. The risk is no greater than HDDs today with their volatile write caches. -- richard > > Richard Jahnel > Network Engineer > On-Site.com | Ellipse Design > 866-266-7483 ext. 4408 > Direct: 669-800-6270 > > > -----Original Message----- > From: OmniOS-discuss [mailto:omnios-discuss-boun...@lists.omniti.com] On > Behalf Of Chris Siebenmann > Sent: Wednesday, March 23, 2016 9:36 AM > To: Fred Liu <fred_...@issi.com> > Cc: omnios-discuss@lists.omniti.com > Subject: Re: [OmniOS-discuss] 4kn or 512e with ashift=12 > >>> The sd.conf whitelist also requires a reboot to activate if you need >>> to add a new entry, as far as I know. >>> >>> (Nor do I know what happens if you have some 512n disks and >>> some 512e disks, both correctly recognized and in different >>> pools, and now you need to replace a 512n disk with a spare 512e >>> disk so you change sd.conf to claim that all of the 512e disks >>> are 512n. I'd like to think that ZFS will carry on as normal, >>> but I'm not sure. This makes it somewhat dangerous to change >>> sd.conf on a live system.) >> >> There are two cases if we don't use the remedy (whitelist in illumos >> or -o ashift in ZoL) here: >> a): 512n <---> 512e. This replacement should work *in theory* if the >> lie works *correctly*. > > This will not work without the sd.conf workaround in Illumos. > > All 512e disks that I know of correctly report their actual physical disk > size to Illumos (and to Linux/ZoL). When a disk reports a 4K physical sector > size, ZFS will refuse to allow it into an ashift=9 vdev *regardless* of the > fact that it is 512e and will accept reads and writes in 512-byte sectors. > > In Illumos, you can use sd.conf to lie to the system and claim that this is > not a 512e but a 512n disk (ie, it has a 512 byte physical sector size). I > don't believe there's an equivalent on ZoL, but I haven't looked. > > This absolute insistence on ZFS's part is what makes ashift=9 vdevs so > dangerous today, because you cannot replace existing 512n disks in them with > 512e disks without (significant) hackery. > > (Perhaps I'm misunderstanding what people mean by '512e' here; I've been > assuming it means a disk which reports 512 byte logical sectors and 4k > physical sectors. Such disks are what you commonly get today.) > > - cks > _______________________________________________ > OmniOS-discuss mailing list > OmniOS-discuss@lists.omniti.com > http://lists.omniti.com/mailman/listinfo/omnios-discuss > _______________________________________________ > OmniOS-discuss mailing list > OmniOS-discuss@lists.omniti.com > http://lists.omniti.com/mailman/listinfo/omnios-discuss _______________________________________________ OmniOS-discuss mailing list OmniOS-discuss@lists.omniti.com http://lists.omniti.com/mailman/listinfo/omnios-discuss
