From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: Direct disk access on IBM Server Date: Thu, 21 Apr 2011 13:00:39 +0200 Message-ID: References: <4DADEBC3.9060404@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 21/04/11 05:50, Ryan Wagoner wrote: > On Wed, Apr 20, 2011 at 7:24 AM, David Brown wrote: >> Pros for hardware raid: >> >> + It can have battery backup (I don't have one at the moment - I have an >> excellent UPS for the whole system). >> + Rebuilds will be handled automatically by just adding new disks >> + The card supports online resizing and reshaping >> + It looks like the card supports caching with an SSD >> + The card supports snapshots of the virtual drives > > Unless the card allows you to enable the write cache without the > backup battery you will not see the real performance of the card. This > option is normally locked out to prevent data loss in case the system > crashes, power is pulled, etc. An external UPS will not protect in all > cases if you enable the write back cache without battery. > The write cache is allowed without the battery, but disabled by default. I agree that even with an UPS there is still a risk - I guess that's why it is disabled. But the risk is pretty minimal for me - there is no realistic chance of the power plug being pulled, for example. Other risks do exist - the power supply on the server may fail, the UPS may fail, etc. In the end there are /always/ risks - even with a battery on the raid card, it won't protect against everything. All I can do is reduce the risks to a realistic minimum while keeping good performance and features (and sensible cost!), and make sure I've got good backups of everything. > I have systems with both software raid and hardware raid. If the > budget allows I tend to go the hardware raid route. When buying a > Dell, HP, etc server with hardware raid you end up with a complete > package. The enclosure, card, and server monitoring software make it > easy to manage and visually see which drive has failed. > > Ryan > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >