Re: [zfs-discuss] SLOG striping? (Bob Friesenhahn)
The term 'stripe' has been so outrageously severely abused in this forum that it is impossible to know what someone is talking about when they use the term. Seemingly intelligent people continue to use wrong terminology because they think that protracting the confusion somehow helps new users. We are left with no useful definition of 'striping'. There is no striping. (I'm sorry, I couldn't resist.) ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping? (Bob Friesenhahn)
On Jun 22, 2010, at 8:40 AM, Jeff Bacon ba...@walleyesoftware.com wrote: The term 'stripe' has been so outrageously severely abused in this forum that it is impossible to know what someone is talking about when they use the term. Seemingly intelligent people continue to use wrong terminology because they think that protracting the confusion somehow helps new users. We are left with no useful definition of 'striping'. There is no striping. (I'm sorry, I couldn't resist.) There is no spoon ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
[zfs-discuss] SLOG striping?
Hi all I plan to setup a new system with four Crucial RealSSD 256MB SSDs for both SLOG and L2ARC. The plan is to use four small slices for the SLOG, striping two mirrors. I have seen questions in here about the theoretical benefit of doing this, but I haven't seen any answers, just some doubt about the effect. Does anyone know if this will help gaining performance? Or will it be bad? Vennlige hilsener / Best regards roy -- Roy Sigurd Karlsbakk (+47) 97542685 r...@karlsbakk.net http://blogg.karlsbakk.net/ -- I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og relevante synonymer på norsk. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
On Mon, 21 Jun 2010, Roy Sigurd Karlsbakk wrote: I plan to setup a new system with four Crucial RealSSD 256MB SSDs for both SLOG and L2ARC. The plan is to use four small slices for the SLOG, striping two mirrors. I have seen questions in here about the theoretical benefit of doing this, but I haven't seen any answers, just some doubt about the effect. Does anyone know if this will help gaining performance? Or will it be bad? I don't know anything about these SSDs but if they might lose the last record or two then striping would be bad since it would cause more writes to be lost. Data would only be recovered up to the first point of loss, even though some newer data is still available on a different SSD. Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer,http://www.GraphicsMagick.org/ ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
Roy Sigurd Karlsbakk wrote: Hi all I plan to setup a new system with four Crucial RealSSD 256MB SSDs for both SLOG and L2ARC. The plan is to use four small slices for the SLOG, striping two mirrors. I have seen questions in here about the theoretical benefit of doing this, but I haven't seen any answers, just some doubt about the effect. Does anyone know if this will help gaining performance? Or will it be bad? I'm planning to do something similar, though I only want to install 2 devices. Some thoughts I had so far: - mirroring l2arc won't gain anything, as it doesn't contain any information that cannot be rebuilt if a device is lost. Further, if a device is lost, the system just uses the remaining devices. So I wouldn't waste any space mirroring l2arc, I'll just stripe them. - the purpose of a zil device is to reduce latency. Throughput is probably not an issue, especially if you configure your pool so that large writes go to the main pool. As 2 devices don't have a lower latency than one, I see no real point in striping slog devices. - For slog you need SSD with supercap which are significantly more expensive than without. I'll try the OCZ Vertex 2 Pro in the next few days and can give a report how it performs. For L2ARC cheap MLC SSDs will do. So if I had the chance to buy 4 devices, I'd probably buy 2 different sets. 2 cheap large L2ARC devices, 2 fast supercapped small ones. The 2 slog devices would go into a mirror, the L2ARC devices in a stripe. I'd probably take the remaining space of the slog devices into the stripe, too, though this might affect write performance. Just me thoughts... -- Arne Vennlige hilsener / Best regards roy -- Roy Sigurd Karlsbakk (+47) 97542685 r...@karlsbakk.net http://blogg.karlsbakk.net/ -- I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og relevante synonymer på norsk. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
- mirroring l2arc won't gain anything, as it doesn't contain any information that cannot be rebuilt if a device is lost. Further, if a device is lost, the system just uses the remaining devices. So I wouldn't waste any space mirroring l2arc, I'll just stripe them. I don't plan to attempt to mirror L2ARC. Even the docs say it's unsupported, so no point of that. - the purpose of a zil device is to reduce latency. Throughput is probably not an issue, especially if you configure your pool so that large writes go to the main pool. As 2 devices don't have a lower latency than one, I see no real point in striping slog devices. My guess was a striped setup could give me 2xIOPS if SLOG is designed to do this. Any idea if it is? - For slog you need SSD with supercap which are significantly more expensive than without. I'll try the OCZ Vertex 2 Pro in the next few days and can give a report how it performs. For L2ARC cheap MLC SSDs will do. hm... Last I checked those OCZ Vertexes were on the both large and expensive side. What do you pay for a couple of small ones? We'll be installing 48 gigs of memory in this box, but I doubt we'll need more than 4GB SLOG in terms of traffic. So if I had the chance to buy 4 devices, I'd probably buy 2 different sets. 2 cheap large L2ARC devices, 2 fast supercapped small ones. The 2 slog devices would go into a mirror, the L2ARC devices in a stripe. I'd probably take the remaining space of the slog devices into the stripe, too, though this might affect write performance. Any idea if something like a small, decently priced, supercapped SLC SSD exist? Vennlige hilsener / Best regards roy -- Roy Sigurd Karlsbakk (+47) 97542685 r...@karlsbakk.net http://blogg.karlsbakk.net/ -- I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og relevante synonymer på norsk. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
On Mon, Jun 21, 2010 at 11:24 AM, Roy Sigurd Karlsbakk r...@karlsbakk.net wrote: Any idea if something like a small, decently priced, supercapped SLC SSD exist? The new OCZ Deneva drives (or others based on the SF-1500) should work well, but I don't know if there's pricing available yet. -B -- Brandon High : bh...@freaks.com ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
Roy Sigurd Karlsbakk wrote: - mirroring l2arc won't gain anything, as it doesn't contain any information that cannot be rebuilt if a device is lost. Further, if a device is lost, the system just uses the remaining devices. So I wouldn't waste any space mirroring l2arc, I'll just stripe them. I don't plan to attempt to mirror L2ARC. Even the docs say it's unsupported, so no point of that. Oops, makes sense ;) - For slog you need SSD with supercap which are significantly more expensive than without. I'll try the OCZ Vertex 2 Pro in the next few days and can give a report how it performs. For L2ARC cheap MLC SSDs will do. hm... Last I checked those OCZ Vertexes were on the both large and expensive side. What do you pay for a couple of small ones? We'll be installing 48 gigs of memory in this box, but I doubt we'll need more than 4GB SLOG in terms of traffic. 50GB for 400 Euro. They are MLC flash, but, as someone in a different thread pointed out, they have 3 years warranty ;) My hope is that they last long enough until cheaper options become available. My major concern is that if I buy two identical models they'll break the same day. This is not purely hypothetical. If they internally just count the write cycles and trigger a SMART fail if a certain threshold is reached, exactly this will happen. -- Arne ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- boun...@opensolaris.org] On Behalf Of Roy Sigurd Karlsbakk I plan to setup a new system with four Crucial RealSSD 256MB SSDs for both SLOG and L2ARC. The plan is to use four small slices for the SLOG, striping two mirrors. I have seen questions in here about the theoretical benefit of doing this, but I haven't seen any answers, just some doubt about the effect. Does anyone know if this will help gaining performance? Or will it be bad? log and cache devices don't stripe. You can add more than one, and the syntax is the same as if you were going to create a stripe in the main pool, but the end result is round-robin for log cache devices. It's tough to say how much this will benefit performance, unless you try it. PS. I'm only repeating what I believe to have learned by older posts on this list. I didn't go read the code myself or anything like that, so I acknowledge some possibility that something I've said is wrong. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
On Jun 21, 2010, at 11:17 AM, Arne Jansen wrote: Roy Sigurd Karlsbakk wrote: Hi all I plan to setup a new system with four Crucial RealSSD 256MB SSDs for both SLOG and L2ARC. The plan is to use four small slices for the SLOG, striping two mirrors. I have seen questions in here about the theoretical benefit of doing this, but I haven't seen any answers, just some doubt about the effect. Does anyone know if this will help gaining performance? Or will it be bad? I'm planning to do something similar, though I only want to install 2 devices. Some thoughts I had so far: - mirroring l2arc won't gain anything, as it doesn't contain any information that cannot be rebuilt if a device is lost. This is not properly stated. There is nothing in the L2ARC that is not also in the pool, so it is simply a cache. You are correct in that the L2ARC is not rebuilt, but you miss the reason why the rebuild is not necessary (or desired) Further, if a device is lost, the system just uses the remaining devices. So I wouldn't waste any space mirroring l2arc, I'll just stripe them. Yes, this is the most economical solution. - the purpose of a zil device is to reduce latency. The purpose of a separate device is to reduce latency for synchronous writes. Throughput is probably not an issue, especially if you configure your pool so that large writes go to the main pool. As 2 devices don't have a lower latency than one, I see no real point in striping slog devices. Striping separate log devices can help for high transaction rate environments or where the latency is constrained by bandwidth. - For slog you need SSD with supercap which are significantly more expensive than without. I'll try the OCZ Vertex 2 Pro in the next few days and can give a report how it performs. For L2ARC cheap MLC SSDs will do. For a separate log, choose a device which honors cache flush commands. Nonvolatile caches are nice, but rare -- HDDs do act well as ZIL devices, but almost never have nonvolatile caches. -- richard -- Richard Elling rich...@nexenta.com +1-760-896-4422 ZFS and NexentaStor training, Rotterdam, July 13-15, 2010 http://nexenta-rotterdam.eventbrite.com/ ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] SLOG striping?
On Mon, 21 Jun 2010, Edward Ned Harvey wrote: log and cache devices don't stripe. You can add more than one, and The term 'stripe' has been so outrageously severely abused in this forum that it is impossible to know what someone is talking about when they use the term. Seemingly intelligent people continue to use wrong terminology because they think that protracting the confusion somehow helps new users. We are left with no useful definition of 'striping'. The slog does actually 'stripe' in some cases (depending on what 'stripe' means) if you study how it works in sufficient detail. At least that is what we have been told. The slog does not do micro-striping, nano-striping, pico-striping, or femto-striping (not even at the sub-bit level) but it does do mega-striping. Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer,http://www.GraphicsMagick.org/ ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
