Ahmed Kamal wrote:
>
>
> So, performance aside, does SAS have other benefits ? Data
> integrity ? How would a 8 raid1 sata compare vs another 8 smaller
> SAS disks in raidz(2) ?
> Like apples and pomegranates. Both should be able to saturate a
> GbE link.
>
>
> You're the expert, but isn't the 100M/s for streaming not random
> read/write. For that, I suppose the disk drops to around 25M/s which
> is why I was mentioning 4 sata disks.
>
> When I was asking for comparing the 2 raids, It's was aside from
> performance, basically sata is obviously cheaper, it will saturate the
> gig link, so performance yes too, so the question becomes which has
> better data protection ( 8 sata raid1 or 8 sas raidz2)
Good question. Since you are talking about different disks, the
vendor specs are different. The 500 GByte Seagate Barracuda
7200.11 I described above is rated with an MTBF of 750,000 hours,
even though it comes in either a SATA or SAS interface -- but that isn't
so interesting. A 450 GByte Seagate Cheetah 15k.6 (SAS) has a rated
MTBF of 1.6M hours. Putting that into RAIDoptimizer we see:
Disk RAID MTTDL[1](yrs) MTTDL[2](yrs)
----------------------------------------------------
Barracuda 1+0 284,966 5,351
z2 180,663,117 6,784,904
Cheetah 1+0 1,316,385 126,839
z2 1,807,134,968 348,249,968
For ZFS, 50% space used, logistical MTTR=24 hours, mirror
resync time = 60 GBytes/hr
In general, (2-way) mirrors are single parity, raidz2 is double parity.
If you use a triple mirror, then the numbers will be closer to the raidz2
numbers.
For explanations of these models, see my blog,
http://blogs.sun.com/relling/entry/a_story_of_two_mttdl
-- richard
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