Date: Mon, 15 Feb 2010 00:30:27 -0800 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: freebsd-stable@freebsd.org Subject: Re: hardware for home use large storage Message-ID: <20100215083027.GA51038@icarus.home.lan> In-Reply-To: <20100215085710.21077b9vaoqxbpgk@webmail.leidinger.net> References: <cf9b1ee01002140653m7b20f60bv12b399d80bd92d9a@mail.gmail.com> <4B786D3A.3000408@langille.org> <cf9b1ee01002141442n283e4f87s50bfd3bf3c69ec60@mail.gmail.com> <cf9b1ee01002141510p7d2d3fddg2a41113af89cbe6e@mail.gmail.com> <20100215085710.21077b9vaoqxbpgk@webmail.leidinger.net>
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On Mon, Feb 15, 2010 at 08:57:10AM +0100, Alexander Leidinger wrote: > Quoting Dan Naumov <dan.naumov@gmail.com> (from Mon, 15 Feb 2010 > 01:10:49 +0200): > > >Get a dock for holding 2 x 2,5" disks in a single 5,25" slot and put > >it at the top, in the only 5,25" bay of the case. Now add an > >additional PCI-E SATA controller card, like the often mentioned PCIE > >SIL3124. Now you have 2 x 2,5" disk slots and 8 x 3,5" disk slots, > >with 6 native SATA ports on the motherboard and more ports on the > >controller card. Now get 2 x 80gb Intel SSDs and put them into the > >dock. Now partition each of them in the following fashion: > > > >1: swap: 4-5gb > >2: freebsd-zfs: ~10-15gb for root filesystem > >3: freebsd-zfs: rest of the disk: dedicated L2ARC vdev > > If you already have 2 SSDs I suggest to make 4 partitions. The > additional one for the ZIL (decide yourself what you want to speed > up "more" and size the L2ARC and ZIL partitions accordingly...). > This should speed up write operations. The ZIL one should be zfs > mirrored, because the ZIL is more sensitive to disk failures than > the L2ARC: zpool add <pool> log mirror <SSD1pX> <SSD2pX> > > >GMirror your SSD swap partitions. > >Make a ZFS mirror pool out of your SSD root filesystem partitions > >Build your big ZFS pool however you like out of the mechanical > >disks you have. > >Add the 2 x ~60gb partitions as dedicated independant L2ARC devices > >for your SATA disk ZFS pool. > > BTW, the cheap way of doing something like this is to add a USB > memory stick as L2ARC: > http://www.leidinger.net/blog/2010/02/10/making-zfs-faster/ > This will not give you the speed boost of a real SSD attached via > SATA, but for the price (maybe you even got the memory stick for > free somewhere) you can not get something better. I had a feeling someone would bring up L2ARC/cache devices. This gives me the opportunity to ask something that's been on my mind for quite some time now: Aside from the capacity different (e.g. 40GB vs. 1GB), is there a benefit to using a dedicated RAM disk (e.g. md(4)) to a pool for L2ARC/cache? The ZFS documentation explicitly states that cache device content is considered volatile. Example: # zpool status storage pool: storage state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM storage ONLINE 0 0 0 mirror ONLINE 0 0 0 ad10 ONLINE 0 0 0 ad14 ONLINE 0 0 0 errors: No known data errors # mdconfig -a -t malloc -o reserve -s 256m -u 16 # zpool add storage cache md16 # zpool status storage pool: storage state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM storage ONLINE 0 0 0 mirror ONLINE 0 0 0 ad10 ONLINE 0 0 0 ad14 ONLINE 0 0 0 cache md16 ONLINE 0 0 0 And removal: # zpool remove storage md16 # mdconfig -d -u 16 # -- | Jeremy Chadwick jdc@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB |
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