Date: Mon, 27 Jan 2014 18:15:28 +0000 From: Kaya Saman <kayasaman@gmail.com> To: krad <kraduk@gmail.com> Cc: freebsd-questions <freebsd-questions@freebsd.org>, =?ISO-8859-1?Q?Trond_Endrest=F8l?= <Trond.Endrestol@fagskolen.gjovik.no> Subject: Re: ZFS confusion Message-ID: <52E6A240.8010404@gmail.com> In-Reply-To: <CALfReyf_V%2B9iWrPTceHya9GnW3c6_aNA%2BEt8ZzJQypNsHrriNQ@mail.gmail.com> References: <52E40C82.7050302@gmail.com> <alpine.BSF.2.00.1401270944100.4811@mail.fig.ol.no> <52E62DFF.3010600@gmail.com> <alpine.BSF.2.00.1401271149160.4811@mail.fig.ol.no> <52E6463C.6090805@gmail.com> <alpine.BSF.2.00.1401271309090.4811@mail.fig.ol.no> <52E6537F.8020907@gmail.com> <CALfReyeO0sOAHLp2y_FpxT-yAUoqSdrtdbjQG_EEOzNL33q1XQ@mail.gmail.com> <52E6657E.1050103@gmail.com> <CALfReyf_V%2B9iWrPTceHya9GnW3c6_aNA%2BEt8ZzJQypNsHrriNQ@mail.gmail.com>
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Many thanks I really appreciate the advice :-) Best Regards, Kaya On 01/27/2014 04:52 PM, krad wrote: > Look into under provisioning the SSD drives as well, this can preserve > write performance in the long term and decrease write wear. Looking at > the number of drives, and general spec of what you are putting > together, I would try to stretch to 256 GB ssd but only provision them > to use say 128-160 GB of the capacity. > > I'm not 100% sure this is still all necessary now as TRIM support is > much better now under zfs but here is how i did my ssd drives under > linux. You may well be able to do it under freebsd but I havent > figured out how. > > root@ubuntu-10-10:~# hdparm -N /dev/sdb > > /dev/sdb: > max sectors = 312581808/312581808, HPA is disabled > > root@ubuntu-10-10:~# hdparm -Np281323627 /dev/sdb > > /dev/sdb: > setting max visible sectors to 281323627 (permanent) > Use of -Nnnnnn is VERY DANGEROUS. > You have requested reducing the apparent size of the drive. > This is a BAD idea, and can easily destroy all of the drive's contents. > Please supply the --yes-i-know-what-i-am-doing flag if you really want this. > Program aborted. > > root@ubuntu-10-10:~# hdparm -Np281323627 --yes-i-know-what-i-am-doing /dev/sdb > > /dev/sdb: > setting max visible sectors to 281323627 (permanent) > max sectors = 281323627/312581808, HPA is enabled > > root@ubuntu-10-10:~# > > > On 27 January 2014 13:56, Kaya Saman <kayasaman@gmail.com > <mailto:kayasaman@gmail.com>> wrote: > > Many thanks for the explanation :-) > > > On 01/27/2014 01:13 PM, krad wrote: > > Neither of these setups is ideal, The best practice for your > vdev is to use 2^n + your parity drives > This means in your case with raidz3 you would do something > > 2 + 3 > 4 + 3 > 8 + 3 > > the 1st two are far from ideal as the ratios are low 8 + 3, so > 11 drives per raidz3 vdev would be optimal. This would fit > nicely with your 26 drive enclosure as you would use 2x11 > drive raidz3 vdevs, 2 hot spares, and two devices left for > l2arc/zil. Probably best chop up the ssds, mirror the zil and > stripe the l2arc, assuming you dont want to do down the route > using generic SSD's rather than write/read optimized ones > > > Yep was going to use your suggestion for l2arc/zil on 2x 128GB > Corsair Force Series GS, 2.5" which have quite good w/r speeds - > also I use these on other servers which tend to be quite good and > reliable. > > I think the way to create a mirrored zil and stiped l2arc would be > to use GPT to partition the drives, then use the zfs features > across the partitions. > > > Hmm.... so it also looks like I'm gona have to wait a while for > some more drives then in order to create an 11 disk raidz3 pool. > > > But at least things will be done properly and in a good manner > rather then going down a patch with "no return". > > > > > Regards, > > > Kaya > >
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