Boot DSS V6 on mirrored HDD

[silicon]

We do a lot of Intel serverboards, but don't use software Raid like ESRT2 much at all, due to its need for (and therefore vuneralbility to) OS-level support for correct operation. We either use the midplane + activation key Raid (eg. with SR2500LX), or add-in Raid card (eg. SRCSASJV, ala LSI8888ELP) with SSR212MC2.

The active midplane without activation key ("LSI IT/IR" Raid) may be supported by DSS, would have to verify this. The optional 2 x 2.5" kit for the new SR2600 chassis (eg. SR2620URLX) gives another option, tho you loose the 6th 3.5" drive bay, but I guess that would require the unsupported ERST2 again. Mmmmm. Next option (and they suggest this in the readme), is to create a small Raid array/vd within your main storage Raid array. Eg. if using a single R5, you would 1st create a little 2GB Raid array/vd across the disk group, then allocate the rest for the main array/vd. This config would be fully supported. Cheers.

[itr]

Yes, most montherboard integrated RAID solutions are really Hardware assisted Software RAID, not fully Hardware RAID, so drivers are needed for operation, that is why Open-E does not support it...

I really thing a mirror for Open-E although giving a sence of peace of mind, it's a little overkill... I boot from an IDE compact Flash and I keep a spare one imaged from the main on in case I have any problem with my servers... configuration is not stored on the boot medium but on the primary Volume Group I beliave, so if anything happens to the card I just replace it and everything works just fine, you may need to reactivate though as activation is dependant on the boot medium... You can do the same with USB pen drives...

You can boot from the demo CD and still have all your config and data working while you correct the problem.

[Robotbeat]

Yeah, that's actually one of the coolest things about open-e. The modular nature makes it cake to swap stuff in and out, and the fact that linux (what open-e is based off of) has all the drivers built-in makes it all super easy. The new flash modules that Open-E uses has write-leveling built-in and a Write Endurance of at least 2,000,000 times. (I checked.) That's as good as you're going to get. Remember, a mirror doesn't protect you against a software error. So, it's actually better to have that second flashed module ready, sitting on the shelf (even if it isn't activated, yet).

[silicon]

The new flash modules that Open-E uses has write-leveling built-in and a Write Endurance of at least 2,000,000 times. (I checked.)

Hi Robotbeat, any idea how this compares with an ordinary USB pen drive?

What determines the amount of writing DSS does back to the device, eg. logging.
If it was used in a really simple iSCSI mode (so no logging of any NAS activity), then can we estimate the life of a simple USB pen drive used to boot DSS? Cheers

[Robotbeat]

Well, the cheap USB pen drives have no wear-leveling and use MLC (multi-level cell) NAND-chips, so you're looking at a write-endurance of about 10,000. Open-E had some problems a year or two back with running up against that limit because of logging, etc, but all the latest releases (not sure the first one, but any ones that are build 3278 or later are good) I believe are updated to do less writing to the module. Already, the swap file is put on your volume group disks and not on the module. Plus, the new modules that Open-E has been using for a long time now are amazingly good hardware-wise.

I would recommend AGAINST using the cheapest pen drives. If you use a pen-drive, make sure to use one that has built-in wear-leveling or uses SLC (single-level cell) NAND chips. Your Best Buy sales rep will probably have no idea what you're talking about, so you'll have to do your own research. Also, anytime you plan on rebooting, it's a good idea to have a backup module handy. Or at least a demo-CD. Having a backup will keep the gremlins away...

[silicon]

Thanks Robotbeat.
I just had a quick look at the Kingston "DataTraveler" range of USB pen drives (just as a example of a decent brand), see below. They don't say if they are either MLC or SLC (but we would would guess cheaper MLC yes?), but do mention different Read/Write speeds (in MB/sec) as either: "Standard", 15/6, 20/10, or 24/10, so not sure sure if that hints at the faster ones would be SLC or just diff. speed MLC's. Any idea if DSS loaded on a faster/slower pen drive would have any effect (once booted)? Cheers.

• Wear-Leveling Technology: Kingston Flash storage devices incorporate controllers utilizing advanced wear-leveling technology, which distributes write cycles across the Flash card. Wear-leveling thus extends the useful life of a Flash memory card (for details, please see Kingston Flash Cell Endurance section, next).
• Flash Cell Endurance: For Multi-Level Cell (MLC) Flash, up to 10,000 write cycles
per physical sector. For Single-Level Cell (SLC) Flash, up to 100,000 write cycles per
physical sector.
According to Toshiba, the inventor of Flash memory: “the 10,000 cycles of MLC NAND is
more than sufficient for a wide range of consumer applications, from storing documents to
digital photos. For example, if a 256-MB MLC NAND Flash-based card can typically store
250 pictures from a 4-megapixel camera (a conservative estimate), its 10,000 write/erase
cycles, combined with wear-leveling algorithms in the controller, will enable the user to
store and/or view approximately 2.5 million pictures within the expected useful life of
the card.”1
For USB Flash drives, Toshiba calculated that a 10,000 write cycle endurance would enable
customers to “completely write and erase the entire contents once per day for 27 years,
well beyond the life of the hardware.”
SLC Flash based-products, typically found in Kingston’s Elite Pro™/Ultimate Flash cards
and DataTraveler II, II Plus – Migo Edition and Secure / Secure – Privacy Edition USB Flash
drives, offer both high performance and high endurance.

[itr]

I was looking online for Flash memory with those properties and seems like manufacturers do not publish that level of detail on their flash memory specs...

Even if the put it in the specs it may still be shady as for example, some say "Support Wear Leveling"; Wear leveling algorithms at the beginning were not implemented on the flash controller itself but on the file system level and you needed to used a file system that was designed for flash memory (like exFAT) and a flash memory that supports it... nodays it is implemented on the controller (USB pen drives have a USB flash controller inside) so the wear levelig works even when using FAT.

RobotBeat, soulc you please share with us which USB flash memory have you found to have single level-cell and wear leveling implemeted in the controller?

Also, this may not even be necessary: I checked the compactflash card I have been using in production for a month and found that the only new/modified files on it are the license file and the activation file, which means that on the latest versions, not even logging is done on the card but on the main volume group instead... So the card will only go throuh erase/write cycles whenever you do an version update, I already did 2 updates when testing the V6 betas, so I only have 9,998 updates until I have to replace the card?

In any case it will be good to know which pen drives have those characteristics, I will be migrating from ESX to ESXi botting from USB pen drives soon and here I think will be more necessary...