Comments on: Starwind iSCSI SAN – configuration RAID 1 Mirror and connection to ESX 4

By: Vladan

Vladan — Mon, 19 Oct 2009 13:40:05 +0000

Thanks girtscipulus,

Me too I'm waiting for the version 5 as it should also simplify the installation process with including the Starport Driver in it…!!!

By: girtscipulus

girtscipulus — Mon, 19 Oct 2009 09:23:07 +0000

Great post, Vladan!
Constantin, as I heard in version 5 there will be active-active HA? If yes, then the question about Business Continuity for SMB will be solved.

By: ConstantinV

ConstantinV — Fri, 16 Oct 2009 09:50:59 +0000

Hello! For now I can say, that in StarWind 5.1 we will implement mirrored cache.

By: bj28

bj28 — Thu, 15 Oct 2009 21:23:48 +0000

@NiTRo

Thanks for pointing this out. With, for example, a DL380 G6 you can use Mirrored memory mode or even better Lockstep Mode to minimize the risk and build a very reliable/powerful software-based SAN.

But you've still the SPOF/risk. If the hole server goes down(OS failure, HW failure, etc.) the actual write-cache content isn't saved (or synced to the second node(Starwind?)) and therefore there is the risk of potential data loss.

By: Vladan

Vladan — Thu, 15 Oct 2009 04:05:40 +0000

Thanks bj28 for pointing this out. Maybee someone from Starwind could respond to this? I'm sure the post was seen.... -:)

Nitro: That's right, with memory prices down this might be an option too....

Thanks
Vladan

By: NiTRo

NiTRo — Wed, 14 Oct 2009 23:14:10 +0000

Bj,
you right but you could also use servers with “protected” memory (it's like RAID 1 for RAM if you don't know), you got twice less memory but no SPOF

By: bj28

bj28 — Wed, 14 Oct 2009 20:45:15 +0000

Hi Vladan,

thanks for the great informations in your blog.

I like "software-based" SAN's (Datacore/Starwind) very much, but there is everytime one big problem: The write-cache

Storage vendors normaly use Mirrored Write-Cache/Dual-Controller or you can use BBWC (with very tiny RAM) to protect the write cache.

But the "software-based" SAN's use the server RAM for write-cache.

This creates high risk for potential/guaranteed data loss (faulty RAM or powerloss (can occurs even with a UPS))

Datacore not only mirrors the data volumes. Even the write-cache is mirrored when you have 2 servers (Synchronous Mirroring). So you should not activate write-caching in a Datacore-Environment if you have a single server (because it's not protected).

I can't find any informations how Starwind deals with write-cache protection (or supports write-cache mirroring).

I think everyone should consider this, or live with the (huge) write-performance penalty when not enabling write-cache.

Bj
Greetings from Germany