> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Jim Klimov
> 1) Use a ZFS mirror of two SSDs
> - seems too pricey
> 2) Use a HDD with redundant data (copies=2 or mirroring
> over two partitions), and an SSD for L2ARC (+maybe ZIL)
> - possible unreliability if the only HDD breaks
> 3) Use a ZFS mirror of two HDDs
> - lowest performance
> 4) Use a ZFS mirror of two HDDs and an SD card for L2ARC.
> Perhaps add another "built-in flash card" with PCMCIA
> adapters for CF, etc.
The performance of a SSD or flash drive or SD card is almost entirely
dependent on the robustness/versatility of the built-in controller circuit.
You can rest assured that no SD card and no USB device is going to have
performance even remotely close to a decent SSD, except under the conditions
that are specifically optimized for that device. The manufacturers, of
course, will publish their maximum specs, and the real world usage of the
device might be an order of magnitude lower.
A little while back, I performed an experiment - I went out and bought the
best rated, most expensive USB3 flash drives I could find, and I benchmarked
them against the cheapest USB2 hard drives I could find. The hard drives
won by a clear margin, like 4x to 8x faster, except when running large
sequential "dd" to/from the raw flash device on the first boot - in which
case the flash won by a small margin (like 10%)
Given your hardware limitations, the only way to go fast is to use a SSD,
and the only way to go fast with redundancy is to use a mirror of two SSD's.
If you don't go for the SSD's, then your HDD's will be the second fastest
option. Do not put any SD card into the mix. It will only hurt you.
> Second question regards single-HDD reliability: I can
> do ZFS mirroring over two partitions/slices, or I can
> configure "copies=2" for the datasets. Either way I
> think I can get protection from bad blocks of whatever
> nature, as long as the spindle spins. Can these two
> methods be considered equivalent, or is one preferred
> (and for what reason)?
I would opt for the copies=2 method, because it's reconfigurable if you
want, and it's designed to work within a single pool, so it more closely
resembles your actual usage. If you mirror across two partitions on the
same disk, there may be unintended performance consequences because nobody
expected you to do that when they wrote the code.
> Also, how do other list readers place and solve their
> preferences with their OpenSolaris-based laptops? ;)
I'm sorry to say, there is no ZFS-based OS and no laptop hardware that I
consider to be a reliable combination. Of course I haven't tested them all,
but I don't believe in any of them because it's "unintended, uncharted,
untested, unsupported." I think you'll find the best support for this
subject on the openindiana mailing lists.
After oracle acquired sun, most of the home users and laptop users left the
opensolaris mailing lists in favor of the openindiana lists. The people
that remain here are primarily focused on enterprise and servers.
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