Web Hosting Talk : Web Hosting Main Forums : Dedicated Server : do you use software raid ?

[ttgt]

Hi,

i want to do raid 10 with 4 hd,

i want to run centos/cpanel,

but the hardware raid is expensive,

do you use software raid ? is it safe? lower the performance ?


thanx

[MikeTrike]

Avoid software raid if you intend to run anything more than RAID1. Alternatively if you're using a dedicated system just for RAID storage with a specific piece of software; that's fine also. I assume you're not going to be using it just for storage and will be running other things on it.

Software RAID runs the risk of being corrupted under heavy system load. It will likely have lower performance (depending on the application). It can be safe, again depending on the application, i.e. how you're using the software RAID.

Hardware RAID is expensive for the reason, it offloads all of the RAID to the controller itself. Software RAID uses your server's CPU, which is why putting your server under load, takes that CPU away from RAID work and vice versa.

You'll also have better compatibly with CentOS and a hardware RAID card like Adaptec, 3ware, etc.

There is a lot more involved than what I've noted here. It is definitely not recommended in most cases.

[jhadley]

It will lower the performance of the server somewhat, but if your applications are not CPU intensive and you have a good CPU then it should be fine.

[[CTI] Todd]

Originally Posted by MikeTrike

Avoid software raid if you intend to run anything more than RAID1.

RAID 10 works great as well. RAID levels that require parity calculations I might think twice about because of the increase in CPU usage.

Originally Posted by MikeTrike

Software RAID runs the risk of being corrupted under heavy system load.

In many years of using software RAID I have never had this happen, or heard of it happening to anyone. Is it possible? Yes. Is it also possible for a hardware card to develop problems, yes.

Originally Posted by MikeTrike

Hardware RAID is expensive for the reason, it offloads all of the RAID to the controller itself.

For RAID levels that use parity, this is very true. For levels like 0, 10, software RAID CPU overhead is negligible. Cache becomes the advantage of hardware RAID cards in these situations, not the controller CPU.

Originally Posted by MikeTrike

You'll also have better compatibly with CentOS and a hardware RAID card like Adaptec, 3ware, etc.

Huh??

Originally Posted by MikeTrike

There is a lot more involved than what I've noted here. It is definitely not recommended in most cases.

There are situations where it works very well, and some where it is less than ideal.

[[CTI] Todd]

Originally Posted by ttgt

Hi,
do you use software raid ? is it safe? lower the performance ?
thanx

In my experience it is very safe. Tuned properly, it provides very good performance. Hardware-based RAID can outperform it, but its also generally significantly more expensive. You only need as much performance as you need.

[spaethco]

I prefer software RAID (specifically mdraid) for a number of reasons.

1) Universally portable. You can put your drives in any system with the appropriate drive interface (SATA/SAS) and be back online. In any given DC, the chances of having a box with SATA/SAS interfaces is significantly greater than any loaner / emergency replacement hardware having a RAID card, yet alone your exact model of RAID card.

2) The performance hit is negligible for 90+% of applications.

3) Your possibility of recovering data when (not if) the array falls to a failed / degraded state is infinitely higher. mdadm will let you do things that are wholly unnatural to the way you think about arrays. I've been able to reassemble RAID5 arrays from drives that have been replaced over a series of several days to still recover data from the old drives. You can even recreate an array on top of an existing array should it fail to assemble and still recover data because only the defined parity space is overwritten. Try that with an Adaptec card and your data is gone as soon as it starts writing 0's to initialize the array.

[MikeTrike]

Originally Posted by Todd

In many years of using software RAID I have never had this happen, or heard of it happening to anyone. Is it possible? Yes. Is it also possible for a hardware card to develop problems, yes.

I've definitely seen this happen; it's not pretty; to be fair he was running RAID5.

Originally Posted by Todd

Huh??

Yeah scratch that part, for some reason my brain went from CentOS to Citrix vs. VMware; no clue.

[quad3datwork]

If you are using non-parity RAID levels, IMHO the only major advantages when compared to HW RAID CTL are missing on-board cache and BBU.

I haven't seen data recovery failed on HW and SW RAID yet (*knock on wood*). But I do prefer SW (mdadm) recovery process because you need to know what to do, procedures wise so in a sense you have more control over.

See Sun Unified Storage. ZFS is robust. I don't believe Oracle would leverage unreliable SW RAID in enterprise products. Don't need to find articles about people have failed and can't recovery ZFS arrays. Those are far in-between and I haven't seen it myself yet. Same can be said about HW RAID - HW RAID CTL does some funky stuff sometimes as well. Plus ZFS (Solaris 10+; depend on rev level) have iSCSI built-in, great way to make it el-cheapo SAN shares.


All really comes down what you are comfortable with and a piece of mind.