I wanted to build a small back up (maybe also NAS) server using
OpenSolaris and ZFS using consumer drives but after reading a number of
threads and blogs I'm totally confused and was hoping I could get some
questions answered since many people have been using consumer drives
with zfs.
When ZFS first was announced I remember reading that it's error
correction could make consumer level disks suitable for RAID
applications but that doesn't seem to be the case. I'm familiar and have
had good experience with WD drives so I'll be mainly referring to them.
1. WD Caviar Black
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Can they be used with in raidz or mirrors?
With the new models the firmware is locked and you can't change the TLER
settings. When a drive detects an error it's going to hang a long time
trying to correct the problem before it reports the error to ZFS right?
What type of errors are we talking about, bad blocks or something more
serious?
Once it reports an error zfs marks the drive as offline? In the case of
something like bad blocks, can the drive somehow be salvaged by marking
off the bad blocks and reducing the size of the vdev or does it need to
be replaced?
Because of the TLER issue, does this mean that drives that would have
been able to remain in service as just an ordinary stand alone drive
would need to be replaced so that you can expect to replace consumer
drives like the WD Caviar Blacks to not last as long using ZFS?
2. WD Caviar Greens
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I was hoping to use low power drives like the WD Caviar Greens. In
addition to the TLER issue they have an issue with too many load/unload
cycles that would wear out the drive faster when used in raid configs
including zfs. WD put out a utility that could increase the time to
reduce the load/unload cycles (wdidle.exe). Does this still work with
the caviar green drives? Even if it does work, changing the idle
behavior is going to make it use more energy right?
Are Caviar Green drives (the new ones anyway) completely unsuitable for
a ZFS based back-up or NAS server?
3. WD Scorpio Blue/Black
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It seems like the greens are out so these might be a better low power
option? These are the 2.5" SATA laptop drives. These seem like a great
drive to use in a small backup server because of their size and power
usage. If you don't need large capacity but want multiple drives for
redundancy could these be used? Storage density isn't so bad considering
you can fit 2 in the space of one 3.5" drive.
It would be great if these drives could be used but I haven't been able
to find much info using them with zfs. To be able to save money and
space it would be nice to at least have the option of using 2 of these
mirrored as the rpool.
The 5400RPM Scorpio Blue drives with their low power requirements and
low heat would make a nice home backup server if they could work with
ZFS. I've read about people using them in a RAID0 config in their
laptops so maybe there's hope? There's a 1TB Scorpio blue that uses
"Advanced Formatting" (whatever that is) will that be a problem for ZFS?
4 of them can fit in 1 5.25" bay and cost around $700 for 3TB.
4. Consumer vs High End Controllers
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I read a something along the lines of 'you can use consumer drives with
low end sata cards but the enterprise drives like the RE3 and
Velociraptor need to be used with high end sata raid cards'.
Can someone clarify this for me please? I was planning on using
something like the Syba SY-PCI40010
(http://www.newegg.com/Product/Product.aspx?Item=N82E16816124028&cm_re=Sil3124-_-16-124-028-_-Product)
which uses a SiL3124 chipset. I'm not great with this type of hardware
but my understanding is that even though it has RAID features it's a
software raid card and when you don't use the RAID features it's just a
plain SATA port multiplier.
This really confused me because I thought any hardware or software raid
card is just a sata port replicator when you're not letting the card do
the RAID.
In terms of performance, problems, reliability, drive life, what can I
expect under the 4 variations:
SiL Controller with caviar drives?
Sil Controller with RE3 drives?
High end raid controller with caviar drives?
High end raid controller with RE3 drives?
5. Mirror vs raidz
**********************
Can any of the issues with consumer drives be reduced using one type of
vdev over the other? Will adding a seperate log or cache device help?
For a backup server, which would you choose, 4 drives in raidz, 4 drives
in raidz2, 3 drives in raidz with hs, 4 drives with 2 mirrored pairs?
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