[zfs-discuss] Single SSD or raidz with L2arc for zfs root pool
gordan.bobic at gmail.com
Thu Oct 31 10:09:01 EDT 2013
Really? I have rootfs on a USB stick and have had it on all of my ZFS
storage servers dating back to when the only POSIX ZFS implementation was
the KQ one, and none of my USB sticks have failed yet.
On Thu, Oct 31, 2013 at 2:05 PM, Schlacta, Christ <aarcane at aarcane.org>wrote:
> I had mirrored usb root on one system for less than a year with low write
> throughput, and the uptime alone killed both drives. Be wary of this
> On Oct 31, 2013 5:09 AM, "Gregor Kopka" <gregor at kopka.net> wrote:
>> Am 31.10.2013 08:46, schrieb Ivan Krutskikh:
>>> Hi all.
>>> I'm deploying a number of zfs-based storage servers focused on
>>> sequential writes (video surveillance) with a single ssd and a raidz2 group
>>> of 6-7 HDD's
>>> Basically, I have 2 options for my root zfs dataset:
>>> 1)place one the whole zpool on second partition on the ssd.
>>> pro: faster, writes and reads are separated on different devices
>>> cons: single point of failure. underused- the zfs partition with os
>>> consumes about 4G, compared to 80G ssd
>>> 2) place everything on raidz2, boot from first partition of ssd, attach
>>> the second one as l2arc to raidz2.
>>> pro: safer (no single point of failure), better utilized.
>>> cons: more complex setup, possible degradations on resilver events,
>>> longer bootup time.
>>> Which way should I go?
>> With video streams you'll most likely have a relatively constant write
>> load on the pool, if L2ARC makes sense depends on how (and if) the data is
>> read back + how much RAM you have to hold metadata (so you won't have the
>> impact of zfs seeking it), using the SSD as ZIL might make sense in case
>> you have bursty writes or need to buffer the performance impact of read
>> spikes - but the only way to find a good .
>> Since the rpool should be fairly static, small and most likly idle after
>> boot you could as well partition off a bit from each HDD for a mirrored
>> rpool to have redundancy to boot from, but should you really need to reboot
>> quickly to not let evildoers (or whatever you're taping) escape: add (a)
>> fast USB3 stick(s) as mirror(s) to the SSD rpool for cheap redundancy - or
>> mirror the rpool over USB sticks in the first place so you can do away with
>> the SSD should you please.
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